HUGE PACK: IGCSE Flashcards
1
Q
functions of all living organisms:
A
M ovement: can change position
R eproduction: can have offspring either sexually or asexually
S ensitivity: can detect stimuli, such as light, and respond to them
C ontrol: can control their internal environment (homeostasis)
G rowth: can increase mass
R espiration: can produce energy either aerobically or anaerobically
E exretion: can remove toxic waste produced, produced by reactions in the body
N utrition: can absorb nutrients in order to use them for growth and repair
2
Q
eukaryotic organisms:
A
-> eukaryotes are organisms that have a nucleus and organelles that are found within a plasma membrame
-plants
-animals
-fungi
-protoctists
3
Q
plants: characteristics
A
e.g. cereals (such as maize) or herbaceous legume (such as peas)
-multicellular organisms
-cells contain chlorplasts which is the site of photosynthesis: chlorophyll pigments within the chloroplast structure absorb light from the Sun
-they store carbohydrates as starch or sucrose
4
Q
animals: characteristics
A
e.g. mammals (such as humans) and insects (such as flies)
-multicellular organsisms
-cannot photosynthesise
-don’t have cell walls
-most have nervous systems in order to coordinate movement
-store carbohydrates as glycogen
5
Q
fungi: characteristics
A
e.g. yeast (single-celled) and mucor (has the typical hyphal structure)
-some are single-celled
-others have a body organised into a mycelium of thread-like structures called hyphae which have many nuclei
-cell walls are made of chitin
-feed by extracellular secretion of digestive enzymes which break it down into smaller pieced, which can then be absorbed (saprotrophic nutrition)
-may store carbohydrates as glycogen
6
Q
protoctists: characteristics
A
e.g. amoeba (animal-cell like + live in pond water) and chlorella (plant-cell like)
-they are microscopic and single-celled
-some have features like animal cells
-others are more like plants and have chloroplasts
7
Q
prokaryotic organisms:
A
-> prokaryotes do not have a nucleus or membrame-bound organelles
-bacteria
8
Q
bacteria: characteristics
A
e.g. lactobacillus bulgaris (rod-shaped bacterium used to make yoghurt) and pneumococcus (spherical bacterium that causes pneumonia)
-single-celled and very small
-have a cell wall, cell membrame, cytoplasm and plasmids
-lack a nucleus but have circular choromosomes of DNA
-some can carry out photosynthesis but they mainly eat off of other organisms, either dead or alive
9
Q
pathogens:
A
-> pathogens are disease-causing organisms and can be fungi, bacteria, protoctists or viruses
10
Q
viruses characteristics:
A
e.g. tobacco mosaic virus which prevents chloroplast formation, influenza virus, HIV virus leading to AIDS
-viruses are small particles (much smaller than bacteria)- not living organisms
-they are parasitics -> can only reproduce within living cells, can infect every type of living organisms, hijacks the cell mechanisms to create millions of copies of itself and then spreafs within the host by cell bursting
-they come in a wide variety of shapes and sizes
-do not have a cellular structure but have one type of nucleic acid (either DNA or RNA) and a protein coat
11
Q
pathogens: other pathogens
A
-protoctists: plasmodium that causes malaria
-bacteria: pneumococcus which causes pneumonia
-viruses: influenza virus (which causes the ‘flu’) and HIV (which causes AIDS)
-fungi: causes athlete’s foot but can be treated with fungicides
12
Q
levels of organisation: organelles, cells, tissues, organs and organ systems
A
-organelles: specialised subcellular structures found within living cells
-cells: basic structural unit of a living organism
-tissues: group of cells with similar structures, working together to perform the same function
-organs: group of tissues, working together to perform specific functions
-organ system: group of organs with similar functions, working together to perform body functions
an examples of this would be the respiratory system organ system, containing the lungs (organ), which is made up of epithelial tissue consisting of epithelial cells
13
Q
subcellular structures: found in plant and animal cells
A
-nucleus: contains the genetic material which codes for a particular protein, enclosed in a nuclear membrame
-cytoplasm: liquid substance in which chemical reactions occur, contain enzymes (biological catalysts, i.e. proteins that speed up the rate of reaction), organelles are found in it
-cell membrame: contain receptor molecules to identify and selectively control what enters and leaves the cell
-mitochondria: where aerobic respiration reactions occur, providing energy for the cell
-ribosomes: where protein synthesis occurs, found on a structure called the rough endoplasmic reticulum
14
Q
subcellular structures: found only in plants
A
-chloroplasts: where photosynthesis takes place providing food the plant, contains chlorophyll pigment (which makes it green) which harvests the light needed for photosynthesis
-permanent vacoule: contains cell sap, found within the cyctoplasm, improves cell’s rigidity
-cell wall: made from cellulose, provides strength to the cell
15
Q
biological molecules: carbohydrates
A
-they are made of carbon, oxygen and hydrogen
-they are polymers that break down into simple sugars
16
Q
biological molecules: proteins
A
-they are made of carbon, oxygen, hydrogen, sulfur, nitrogen and phosphorus
-they are polymers that are broken down into its monomers: amino acids
17
Q
biological molecules: lipids
A
-lipids (fats and oils) are made of carbon, oxygen and hydrogen
-they are large polymers that are broken down into 3 fatty acids molecules and a glycerol molecule
18
Q
practical: investigate food samples for the presence of glucose, starch, protein and fat - Test for glucose
A
1) add the sample solution into a test tube
2) add drops of Benedict’s solution into the test tube
3) heat in a water bath at 60-70ºC for 5 minutes
4) take test tube out and record the colour
-if glucose is present the solution will turn brick red
-if glucose is not present that the solution will remain blue
19
Q
practical: investigate food samples for the presence of glucose, starch, protein and fat - Test for starch
A
1) pipette the sample solution into wells or on a tile
2) add drops of iodine solution and leave for 1 minute
3) record any colour change
-if starch is present the solution will turn blue-black
-if starch is not present the solution will remain brown
20
Q
practical: investigate food samples for the presence of glucose, starch, protein and fat - Test for protein
A
1) add the sample solution into a test tube
2) add drops of Biuret solution into the test tube
3) leave for 1 minute and then record the colours
-if protein is present the solution will turn purple
-if protein is not present that the solution will remain blue
21
Q
practical: investigate food samples for the presence of glucose, starch, protein and fat - Test for fat
A
1) add 2cm^3 of ethanol to the test solution
2) add 2cm^3 of distilled water
3) leave for 3 minutes and then record the colour
-if fat is present a milky white emulsion will form
-if fat is not present that the solution will remain colourless
22
Q
enzymes:
A
-> enzymes are biological catalysts (a substance that increases the rate of reaction without being used up)
-they are protein molecules and the shape of the enzyme is vital to its function
-this is because each enzyme has its own uniquely shaped active site where the substrate binds, a simplified way to look at how they work is the Lock and Key Hypothesis:
-the shape of the substrate is complementary to the shape of the active site (enzyme specificity), so when they bond it forms an ezyme-substrate complex
-once bound, the reaction takes place and the products are released from the surface of the enzyme
23
Q
enzymes: effect of temperature
A
-the optinum is around 37ºC (body temperature)
-the rate of reaction increases with an increase in temperature to up to this optimum, but above this temperature it rapidly decreases and eventually the reaction stops
-when the temperature becomes too hot, the bonds in the structure will break
-this changes the shape of the active site, so the substrate can no longer fit in
-the enzyme is said to be denatured and can no longer work
24
Q
practical: investigate how enzyme activity can be affected by changes in temperature
A
1) starch solution is heated to set temperature
2) amylase is added
3) iodine is added to each well after a minute
4) measure the time it takes until the iodine stops turning blue-black (this means that starch is not present as amylase has broken the starch down into glucose)
5) repeat the test with different temperature
25
enzymes: effect of pH
-the optinum pH for most enzymes is 7, but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH
-if the pH is too high or too low, the forces that hold the amino acid chains that make up the protein will be affected
-this will change the shape of the active site, so the subtrate can no longer fit in
-the enzyme is said to be denatured and can no longer work
26
diffusion:
-> diffusion is the spreading out of the particles resulting in a net movement from an area of higher concentration to an area of lower concentration
-it is a passive process as no energy is required
-the molecules have to be small in order to be able to move across, for example oxygen, glucose, amino acids and water, but larger molecules such as starch and proteins cannot
27
diffusion: examples
-single-celled organisms can use diffusion to transport molecules into their body ffrom the air -> this is because they have a relatively large surface area to volume ration. Due to their low metabolic demands, diffusion across the surface of the organism is sufficient enough to meet its needs
-in multicellular organisms the surface area to volume ratio is small so they cannot rely on diffusion alone. Instead, surfaces and organ systems have a number of adaptations that allows molecules to be transported in and out of cells. Examples include alevioli in the lungs, vili in the small intestines and root hair cells in plants
28
factors affecting rate of movement: concentration gradient
-the greater the difference in concentration, the faster the rate of diffusion
-this is because more particles are randomly moving down the gradient than are moving against it
29
factors affecting rate of movement: temperature
-the greater the temperature, the greater the movement particles, resulting in more collisions and therefore a faster rate of diffusion
30
factors affecting rate of movement: surface area:volume
-the greater the surface area, the more space for particles to move through, resulting in a faster rate of diffusion
31
factors affecting rate of movement: distance
-the further the particles have to travel the longer it will take
32
osmosis:
-> osmosis is the movement of water molecules from a more concentrated solution to a less concentrated solution through a partially permeable membrame
-a dilute solution of sugar has a high concentration of water (and therefore a high water potential). A concentrated solution of sugar has low concentration of water (and therefore low water potential). Water moves from a dilute solution to a concentrated solution because it moves from an area of high water potential-down a concentration gradient
-it is passive, as it does not use energy
33
important terms: isotonic, hypertonic & hypotonic
-isotonic: if the concentration of sugar in an external solution is the same as the internal, there will be no movement and the solution is said to be isotonic to the cell
-hypertonic: if the concentration of sugar in external solution is higher than the internal, water moves out, and the solution is said to be hypertonic to the cell
-hypotonic: if the concentration of sugar in an external solution is lower than the internal, water moves in, and the solution is said to be hypotonic to the cell
34
osmosis: examples
-osmosis in animals: if the external solution is more dilute (higher water potential), it will move into animal cells causing them to burst + if the external solution is more concentrated (lower water potential), excess water will leave the cell causing it to become shrivelled
-osmosis in plants: if the external solution is more dilute, water will move into the cell and into the vacuole, causing it to swell, resulting in pressure called tugor (essential in keeping the leaves and stems of plants rigid) + if the external solution is less dilute, water will move out of the cell and they will become soft. Evetually the cell membrame will move away from the cell wall (called plasmolysis) and it will die
35
active transport:
-> active transport is the movement of particles from an area of lower concentration to an area of higher concentration, i.e. against the concentration gradient
-this requires energy from respiration as it is working against the gradient, which is why it is called active
36
active transport: examples
-in root hair cells: they take up water and mineral ions (for healthy growth) from the soil + minerals ions are usually in higher concentrations in the cells, meaning diffusion cannot take place + this requires energy from respiration to work
-in the gut: substances such as glucose and amino acids from your food have to move from your gut into your bloodstream + sometime there can be a lower concentration of sugar molecules in the gut than the blood, meaning diffusion cannot take place + active transport is required to move the sugar to the blood against its concentration gradient
37
practical: investigate diffusion in non-living systems
1) cut a 1cm^3 cube of agar made of sodium hydroxide and phenolphthalein indicator
2) place cube in solution of hydrochloric acid
3) remove the cube and wash with water to stop further reaction
4) cut the cube in half and measure the distance that the acid has caused agar to become colourless from outside inwards
5) repeat the experiment two more times and calculate the mean
6) repeat with different concentrations of hydrochloric acid
38
practical: investigating osmosis in potatoes
1) place different surcrose solutions including 0% for a control, in different boiling tubes
2) dry potato strips on a paper towel and measure the masses
3) place each potato strip into each surcrose solution for 20 minutes and record how the mass changed
4) repeat tests at each solution several times with potato strips of similar masses
39
photosynthesis:
-> photosynthesis is the process of making glucose from sunlight in the leaves of the plant. It is an endothermic reaction in which light energy is converted into chemical energy within the chloroplasts
carbon dioxide + water -(light)> glucose + oxygen
6CO2 + 6H2O -> C6H12O6 + 6O2
40
factors affecting photosynthesis: temperature
-with an increase intemperature, the rate of photosynthesis increases
-however, as the reaction is controlled by enzymes, this trend only continues up to a certain temperature until the enzymes begin to denature and the rate of reaction decreases
41
factors affecting photosynthesis: light intensity
-for most plants, the higher the light intensity, the rate of photosynthesis increases, i.e. it is inversely proportional to the square of the distance: light intensity ∝ 1/distance^2
-e.g. this means that if a lamp is 2 metres away from a plant, then light intensity of the lamp is a 1/4 of its original value -> 1/2^2 = 1/4
42
factors affecting photosynthesis: carbon dioxide concentration
-carbon dioxide is also needed to make glucose
-as the concentration of carbon dioxide increases, the rate of reaction increases
43
leaf structures:
-waxy cuticle: helps to reduce water loss by evaporation and is a protective layer found at the top of the leaf
-upper epidermis: very thin and transparent in order to let light into the palisade mesophyll
-palisade mesophyll: contain lots of chloroplasts so that photosynthesis can happen rapidly
-spongy mesophyll: have lots of air space to allow gases to diffuse in and out of cells faster, as it increases the surface area to volume ratio
-lower epidermis: contains guard cells and stomata (gaps)
-guard cell: kidney-shaped cells that open and close the stomata by absorbing or losing water. When lots of water is available, the cells fill and open stomata
-stomata: where gas exchange and loss of water by evaporation takes place-opens during the day and closes at night
44
mineral ions:
-magnesium: required for chlorophyll production + defiency: causes leaves to turn yellow
-nitrate: required to produce amino acids + defiency: causes stunted growth and turns leaves yellow
45
practical: investigating photosynthesis
-use water plants, such as Elodea which releases bubbles of oxygen when photosynthesising
-a lamp with an LED bulb is set up beside the beaker of water containing the water plant. An LED is best as it will not raise the temperature of the water
-sodium hydrogen carbonate (NaHCO3) is added to the water to supply carbon dioxide
-this can set up can be used to investigate the evolution of oxygen from a water plant
46
practical: investigating the effect of light intensity
1) place pondweed in water and set up a desk lamp next to alongside a ruler so that you can measure the distance between the light and the beaker
2) move the lamp away by 10 cm
3) leave for 5 minutes to allow for the pondweed to adapt
4) cound the number of bubbles given off in 1 minute and record
5) repeat steps 2-4
47
practical: investigating the effect of carbon dioxide
-complete the experiment of light intensity but instead of testing the variable of light intensity by using a lamp, use different concentrations of sodium hydrogen carbonate solution, whilst keeping the other variables the same
48
practical: investigating starch production
1) cover half of a small leaf with foil
2) place the plant on a windowsill for 48 hours so that light can reach it
3) put the leaf in a boiling water to kill and preserve it
4) put the leaf in a boiling tube containing hot ethanol for 10 minutes (this removes the chlorophyll pigment)
5) dip the leaf in boiling water to soften it
6) put leaf in a Petri dish and cover with iodine solution
6) the covered half of the leaf will remain orange-brown, whereas the exposed half will change to blue-black (as iodine solution changes colour in the presence of starch, as photosynthesis turned the glucose into starch for storage)
49
practical: experiment provide photosynthesis requires chlorophyll
-repeat the experiment of starch production but with a variegated leaf
-variegated plants are white and green and only contain chlorophyll in the green parts
-therefore only the green areas of the plant will test positive for starch (i.e. turn blue-black) as a result of photosynthesis occuring
-the white areas that do not contain chlorophyll remain an orange-brown colour
50
a balanced diet: source and function
-carbohydrates: bread, cereal, pasta, rice, potatoes -> a high energy source
-proteins: meat, fish, eggs, pulses -> for growth and repair
-lipids: butter, oil, nutes -> a high energy source and for insulation
-dietary fibres: vegetables, bran -> to provide rouphage to keep food moving through gut-defiency causes constipation
-vitamin A: carrots, green vegatbles -> needed for vision, especially in the dark, and for growth
-vitamin C: citrus fruits, broccoli, peppers -> helps to absorb iron
-vitamin D: margarine, oily fish -> helps to absorb calcium
-calcium: milk -> for bone and teeth strength-deficiency can cause rickets (curving of bones)
-iron: red meat -> needed for haemoglobin-deficiency can cause anaemia
-water: water, juice, milk -> needed for cell reactions to take place
51
factors affecting energy requirements:
-age: energy requirements generally increases as we approach adulthood + energy needs of adults go down as they age
-activity levels: if you are more active then you will need more energy for movement
-pregnancy: energy requirements will increase in order to support growth of the foetus + energy needs also increase due to the extra mass of the baby
52
human alimentary canal: mouth + oesophagus
-> the alimentary canal is the passage food moves through once it has been eaten
mouth:
-mechanical digestion: teeth break up large food pieces into smaller pieces with larger surface area to volume ratio (food bolus)
-chemical digestion: amylase breaks down starch into glucose
-salivary glands produce saliva to lubricate the food bolus so it can be swallowed easily
oesophagus:
-tube from the mouth to the stomach
-food bolus moves down due to unidirectional wave-like contractions (peristalsis) created by circular muscles and longitudinal muscles that create a squeezing action
53
human alimentary canal: pancreas + stomach
pancreas:
-produces carbohydrase, protease and lipase enzymes
-secretes enzymes into the stomach and small intestine
stomach:
-gastric juice is released from stomach lining when it detects food in the stomach
-gastric juice is made of: pepisin -> enzyme breaking down proteins + hydrochloric acid -> makes stomach acidic in order for pepsin to work and to kill any ingested bacteria
-peristalsis also occurs here
-the digested food is now called chyme
54
small intestine: duodenum + ileum
duodenum:
-the first part of the small intestine
-carbohydrases, proteases and lipases digest food here
-bile is released into the duodenum: bile is produced in the liver and stored in the gallbladder, it has 2 roles:
1) it is an alkaline to neutralise the hydrochloric acid which comes from the stomach. The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach
2) it breaks down large drops of fat into smaller ones (emulsifies it). The larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acids faster
-peristalsis also occurs here
ileum:
-lined with vili (finger-like projections) to maximise absorption of digested soluble molecules into blood
-vili have a thin lining, a large network of capillaries and have a large surface area
55
large intestine:
-water is absorbed here, to produce faeces
-faeces is stored in the rectum and then removed through the anus
56
digestive enzymes:
carbohydrates (starch):
-broken down by carbohydrases
-starch -> maltose by amylase
-maltose -> glucose by maltase
proteins:
-broken down by proteases in the stomach and small intestine
-proteins -> amino acids
lipids:
-broken down by lipases
-lipids -> glycerol + 3 fatty acids
57
respiration:
-> respiration occurs in every cell in the body of all living things to supply ATP to cells
-cellular respiration is an exothermic reaction
-two types: aerobic and anaerobic
58
aerobic respiration:
-this uses oxygen
-it yields the most energy
-most of the reactions that make up aerobic respiration occur in the mitochondria
glucose + oxygen -> carbon dioxide + water
C6H12O6 + O2 -> CO2 + H2O
59
anaerobic respiration:
-occurs when there is not enough oxygen
-it does not yield as much energy as aerobic respiration
-it is only used as a last resort, for example during a sprint where it is difficult to breathe in enough oxygen
-the oxidation of glucose is complete
in animals:
glucose (C6H12O6) —> Lactic acid
in plants and yeast cells it is called fermentation:
glucose (C6H12O6) —> ethanol + carbon dioxide (CO2)
-this reaction is used to make bread and alcoholic drinks
60
practical: investigate the evolution of carbon dioxide from respiring seeds or other suitable living organisms
1) connect a capillary tube from the air into a flask containing sodium hydroxide, which will also absorb carbon dioxide
2) connect this flask with a capillary tube to another flask containing hydrogen carbonate indicator (which is red at neutral pH and yellow at low pH, i.e. when carbon dioxide is present)
3) connect the second flask to a third flask containing either germinating seeds or respiring animals, such as worms
4) connect the third flask to another flask containing hydrogen carbonate indicator, such as in step 2
-the sodium hydroxide solution in the first flask will absorb carbon dioxide from the air, which will turn the second flask red, as it will have neutral pH. However, the respiring organism will produce carbon dioxide and will therefore turn the indicator yellow
61
practical: investigate the evolution of heat from respiring seeds or other suitable living
1) use 2 vacuum flasks, one containing living germinating seeds and the other containing dead or boiled seeds (as a control)
2) put a thermometer wrapped in cotton wool (to prevent heat from escaping) to measure temperature
3) measure initial temperature
4) leave seeds for a few days and then measure end temperature
-the live germinating seeds will release a heat due to aerobic respiration and so the temperature will increase
62
structure of thorax:
-ribs: bone ‘cage’ surrounding the lungs to provide protection of internal organs
-intercostal muscle: muscles found between the ribs that control inhalation and exhalation
-diaphragm: muscular dome at the bottom of the thorax that changes the pressure in order to control inhalation and exhalation
-trachea: the windpipe, where air enters the thorax and flows to the lungs
-bronchi: the trachea divides into 2 bronchi-one to each lung
-bronchioles: the bronchi further divide into smaller tubes that connect to the alveoli
-alveoli: tiny air sacs that are the place of gas exchange
-pleural membrames: found on the outside of the lungs and inside of chest cavity to lubricate the lungs-reducing friction when breathing
63
intercostal muscles and diaphragm in ventilation:
-intercostal muscles: inhalation -> contract, exhalation -> relax
-ribcage: inhalation -> up and out, exhalation -> down and in
-diaphragm: inhalation -> contracts downwards, exhalation -> relaxes upwards
-pressure: inhalation -> decreases, exhalation -> increases
-air movement: inhalation -> moves in, exhalation -> moves out
-air moves from areas of high pressure to low pressure, so when the thorax pressure decreases (as a result of increased volume created by the intercostal muscles moving the ribcage up and out and the diaphragm flattening) air moves from the higher pressure air down into the low pressure thorax
64
alveoli adaptations:
-thin cell walls -> once cell thick so there is a shorter distance of diffusion
-folded -> to increase surface area for diffusion
-large network of tiny capillaries -> increases concentration gradient between air in alveoli and the blood, as oxygen can move away in the blood and carbon dioxide can be breathed out
65
gas exchange:
-diffusion is a passive process of the spreading out of small particles resulting in a net movement from an area of higher concentration to an area of lower concentration
-in small single-celled organisms can use diffusion to transport molecules into their body from air-this is because they have a relatively large surface area to volume ratio. Due to their low metabolic demands, diffusion across the surface of the organism is sufficient enough to meet its needs
-however, multicellular organisms have a small surface area to volume ratio so they cannot rely on diffusion alone. Instead, surfaces and organ systems have a number of adaptations that allows molecules to be transported in and out of cells. Examples include alveoli in the lungs, vili in the small intestines and root hair cells in plants
66
phloem adaptations:
-transport sucrose and amino acids between leaves and other parts of plants (translocation) -> they can be stored in parts of plants that
-found in the roots, stems and leaves
-elongated cells with holes in the cell walls (the end walls are called sieve plates)
-many organelles from the cells are removed so cell sap can move through -> however, there are many mitochondria in companion cells which provide the energy the cells require
-food substances can be moved in both directions (translocation), from the leaves where they are made for use, or from storage (underground) to parts of the plant that need it
67
xylem adaptations:
-water travels up xylem from the roots into the leaves of the plant to replace the water that has been lost due to transpiration, xylem is adapted in many ways:
-a chemical called lignin is deposited which causes the cells to die
-these cells then become hollow and join end-to-end to form a continuous tube for water and mineral ions to travel through from the roots
-water molecules are attracted to each other by hydrogen bonding- creating a continuous column of water up the plant
-the water evaporates from the leaves of the plant, creating the transpiration stream
-lignin strengthens the plant to help it withstand the pressure of the water movement
-lignin contains bordered pits, which are holes to allow specific areas for water and therefore minerals to enter the plant
68
composition of blood: plasma
-the liquid which carries the components in the blood, e.g. cells, platelets, amino acids, hormones etc.
-plasma is important for the transport of carbon dioxide, digested food, urea, hormones and heat energy
69
composition of blood: red blood cells
-carry oxygen molecules from the lungs to all the cells in the body
-contain haemoglobin: a red protein that combines with oxygen to allow for transport
-no nucleus: to create more space for haemoglobin
-biconcave shape: to maximise surface area for oxygen to be absorbed
-flexible: so they can fit through very narrow vessels
70
composition of blood: white blood cells
-they are part of the immune system, which is the body’s defence against pathogens
-there are 3 types of WBCs:
1) Phagocytic white blood cells:
-one type of white blood cell can do a process called phagocytosis, where the pathogen is engulfed and killed
-as they are able to do this with any type of pathogen it is a non-specific function
2) producing antibodies (lymphocytes):
-each pathogen has an antigen on their surface, which is a structure which a specific complementary antibody can bind to
-once antibodies begin to bind to the pathogen, the pathogens start to clump together, resulting in it in being easier for white blood cells to find them
-if you become infected again with the same pathogen, the specific complementary antibodies will be produce at a faster rate. The individual will not feel the symptoma of the illness, they are said to be immune
3) producing antitoxins:
-WBCs neutralise the toxins released by the pathogen by binding to them
71
human circulatory system:
-the heart is an organ in the circulatory system, the circulatory system carries oxygen and nutrients to every cell in the body and removes the waste products
-the heart pumps blood around the body in a double circulatory system, this means there are two circuits, mammals require this double system because the metabolic rate is higher and so need a faster system
-system 1: deoxygenated blood flows into the right atrium and then into the right ventricle which pumps it to the lungs to undergo gaseous exchange
-system 2: oxygenated blood flows into the left atrium and then into the left ventricle which pumps oxygenated blood around the body
72
structure of the heart:
-muscular walls to provide a strong heartbeat
-the muscular wall of the left ventricle is thicker because blood needs to be pumped all around the body rather than just to the lung like the right ventricle
-4 chambers that seperate the oxygenated blood from the deoxygenated blood: 2 atria above 2 ventricles below
-valves to make sure blood does not flow backwards
-coronary arteries cover the heart to provide its own oxygenated blood supply
73
structure of the heart: process
1) blood flows into the right atrium through the vena cava, and left atrium through the pulmonary vein
2) the atria contract forcing the blood into the ventricles
3) the ventricles then contract, pushing the blood in the right ventricles into the pulmonary artery to be taken to they lungs, and blood in the left ventricle to the aorta to be taken around the body
4) as this happens, valves close to make sure the blood does not flow backwards
74
structure of blood vessels:
arteries: carry blood AWAY from the heart
-layers of muscle in the walls make them strong
-elastic fibres allow them to stretch
-this helps the vessels withstand the high pressure created by the pumping of the heart
veins: carry blood TOWARDS the heart
-the lumen (the actual tube in which blood flows through) is wide to allow the low pressure blood to flow through
-they have valves to ensure the blood flows in the right direction
capillaries: allow the blood to flow very close to cells to enable substances to move between them
-one cell thick walls create a short diffusion pathway
-permeable walls so substances can move across them
75
heart rate changes: exercise
-when exercising, muscles require energy and so will be respiring at a higher rate
-this means that the heart rate will increase in order for the heart to pump more oxygen and nutrients around the body and to remove the waste carbon dioxide from respiring muscles
-stroke volume will also increase, meaning that the heart will pump more powerfully as well as faster
-when anaerobic respiration occurs during high intensity exercises, such as sprints, an oxygen debt is created. Oxygen is then needed to be transferred around the body quickly so that the lactic acid produced by the anaerobic respiration does not cause muscle cramps
76
heart rate changes: adrenaline
-adrenaline is a hormone produced by the adrenal glands above the kidney
-it is responsible for the ‘fight or flight’ reaction
-increased heart rate to deliver more oxygen to respiring muscles that will be contracting more frequently
-increased breathing rate, so more gas exchange occurs and more oxygen diffuses into the blood and more carbon dioxide diffuses out
-blood flow is diverted away from digestive system and towards respiring muscles
-adrenaline also causes other body changes, such as pupils to dilate to let in more light
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coronary heart disease: CHD
-the coronary arteries supply blood to the heart and in CHD these arteries become blocked, due to a build-up of fatty plaques (astherosclerosis). This can cause ischaemia (lack of blood and oxygen) which can eventually lead to a muscle death and therefore a heart attack
-causes of CHD:
1) poor diet:
-a diet rich in saturated fat increases cholesterol levels, which can increase the chance of fatty plaques building up
-high levels of salt can increase blood pressure which damages the blood vessels and increases the chances of fatty deposists building up
2) smoking:
-nicotine causes narrowing of blood pressure and increases blood pressure, which can increase the chance of a blockage in the coronary arteries
3) stress:
-hormones produced in times of stress can increase blood pressure which can damage the vessel walls
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excretion:
-in flowering plants, carbon dioxide and oxygen are the waste products of metabolism and they diffuse out of the leaf via the stomata
-in the human body, there are three main organs of excretion. The lungs excrete carbon dioxide, the kidneys secrete urea, excess water and salts and the skin excretes water and salts through sweat
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tropism in plants:
-plants need hormones to coordinate and control growth. Examples of these include phototropism, the response to light, and gravitropism or geotropism, the response to gravity
-hormones move from the place they are made to where they are needed in order to produce the appropriate response
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auxins: positive phototropism
-most plants show positive phototropism because they grow towards the light source
-the plant is exposed to light on one side
-auxin, a growth hormone, moves to the shaded side of the shoot
-auxin stimulates cells to grow more here
-this means the shoot bends towards the light
-the plant receives more light, meaning photosynthesis can occur at a faster rate
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auxins: negative gravitropism
-most shoots show negative gravitropism as they grow away from gravity. If a shoot is horizontal:
-auxin moves to the lower side
-the cells of the shoot grow more on the side with most auxin, so it stimulates cells to grow more here
-this makes the shoot bend and grow away from the ground
-this is beneficial as light levels are likely to be higher further away from the ground
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auxins: positive gravitropism
-most roots show positive gravitropism as they grow towards gravity. If a root is horizontal:
-auxin moves to the lower side
-the cells of the root grow more on the side with less auxin, so it stimulates cells to grow on the upper side
-this makes the root bend and grow downwards
-this is beneficial as there are more likely to be increased levels of water and nutrients lower down, and it provides stability for the plant
-when the auxin distribution becomes equal on both sides it grows straight in that directions
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the human nervous system:
-the nervous system is made up of nerve cells that carry impulses around the body
-the endocrine (hormonal) system is made up of glands that produce hormones that stimulate changes in the body
-boths systems require stimuli, receptors and effectors and chemicals are involved in both, but there are also key difference between them
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nervous vs endocrine system:
nervous system:
-type of signal -> electrical
-transmitter -> nerve cells
-speed of response -> very fast
-duration of response -> short
endocrine system:
-type of signal -> chemical
-transmitter -> hormones in bloodstream
-speed of response -> slower
-duration of response -> long
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the CNS:
-the central nervous system (CNS) consists of the brain and the spinal cord. It allows us to make sense of our surroundings and respond to it in order to survive
1) receptor cells in sense organs convert a stimulus (such as a bright light) into an electrical impulse
2) this electrical impulse travels along cells called sensory neurons to the central nervous system (CNS)
3) here, the information is processed and the appropiate response is coordinated, resulting in an electrical impulse being sent along motor neurones to effectors
4) the effectors carry out the response (this may be muscles contracting or glands secreting hormones)
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synapses:
-> a synapse is the gap between two neurons, transmission of impulses across the synapse is chemical and uses neurotransmitters
-neurotransmitters are the chemical released at one end of a nerve fibre
-when an electrical impulse is carried along an axon it triggers the nerve-endings to release neurotransmitters
-this is because the electrical impulse cannot directly travel across the synapse (gap) and so needs to be converted to a chemical and then back to an electrical impulse
-the neurotransmitter diffuses across the synapse and binds to receptor molecule on the next neuron
-this stimulates the second neuron to transmit the electrical impulse
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the reflex arc:
-the reflex arc is a subconscious response to a dangerous stimuli, such as a hot surface
-sometimes an extremely quick response is needed and there is not enough time for it to go through the conscious portion of brain so the CNS is involved instead
1) a stimulus is detected by receptors, such as thermoreceptors in fingerprints detecting heat
2) impulses are sent along a sensory neuron
3) in the CNS the impulse passes to a relay neuron
4) impulses are sent along a motor neuron
5) the impulse reaches an effector resulting in the appropiate response, such as a contraction of the biceps to move the arm away from the heat source
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the eye:
-cornea: the transparent outer part of the eye + it refracts light to reach the retina
-iris: the coloured part of the eye that does not allow light to go through + controls how much light enters eye + in bright light, the circular muscles contract and radial muscles relax to make the pupil smaller, avoiding damage to the retina + in dim light, the circular muscles relax and the radial muscles contract to make the pupils larger, so more light can enter to create a better image
-lens: transparent, biconvex disc that attaches to ciliary muscles by the suspensory ligaments + focuses light onto the retina
-retina: contains light receptors + contains rods (respond to dim light) and cones (respond to colour)
-optic nerve: carries impulses between the eye and the brain
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eyes: accomodation
near object:
-ciliary muscles contract
-suspensory ligaments slacken
-this allows the lens to become fatter so the light is refracted more
-light converges on the retina
distant object:
-ciliary muscles relax
-suspensory ligaments stretch
-this allows the lens to become thin so the light is refracted less
-light concverges on the retina
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temperature regulation: homeostasis
-human body temperature is 37.5 ºC, the thermoregulatory centre which monitors and controls body temperature to ensure it remains this temperature is found in the brain
-has receptors that monitor the temperature of the blood
-has receptors in the skin that send impulses to the thermoregulatory centre
when it is hot:
-sweat (evaporates from skin surface resulting in increased energy transfer away from body) is produced from sweat glands
-vasolidation means more blood flows closer to the surface of the skin, resulting in increased energy transfer from the body
when it is cold:
-sweating stops
-skeletal muscles cobtract rapidly (shivering) to generate heat from respiration
-hair stand on end to create an insulating layer, trapping warm air
-vasconstriction means blood does not flow so close to the surface, resulting in less heat lost
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the endocrine system: source, roles and effects
-hormones are chemical messengers that are secreted by endocrine glands into the bloodstream, where they are transported around the body to receptors on the target organ, the pituitary gland is one of the most important glands
-adrenaline: adrenal gland, prepares the body for ‘fight or flight’ response, increases heart rate and breathing rate
-insulin: pancreas, lowers blood glucose levels, converts glucose in the blood into glycogen for storage in muscles and liver
-testosterone: testes, main sex hormone in males, produces secondary characteristics in males (e.g. hair growth, deeper voice)
-progesterone: ovaries, mantains pregnancy, mantains the uterus lining so that the fertilised egg can implant
-oestrogen: ovaries, main sex hormone in females, produces secondary sexual characteristics in females (e.g. breasts developing) and controls mentrual cycle
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sexual reproduction: advantages
1) produces variation of offspring:
-this means that if the environment changes it is likely that an organism in the species will have a characteristic that allows them to survive (called a survival advantage)
-although some individuals may die, variation decreases the chance of the whole species becoming extinct
2) it allows us to use selective breeding:
-this type of reproduction mixes the genetic information from two organisms
-organisms with different desirable characteristics can be bred to produce offspring with even more desirable characteristics
-this speeds up natural selection
-an examples is to increase food production by breeding two animals with lots of meat
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asexual reproduction: advantages + what fertilisation is
-only one parent needed
-uses less energy and is faster as organisms do not need to find a mate
-in favorable conditions lots of identical offspring can be produced
-> fertilisation involves the fusion of a male and a female gamete to produce a zygote that undergoes cell division and develops into an embryo
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insect-pollinated flowers: adaptations
-petals: large and bright to attract insects
-nectar: scanted with nectar to attract insects
-pollen grains: sticky and in moderate amounts
-anthers: inside flower, stiff and attached so that insects can brush past
-stigma: inside flower, sticky so pollen grains stick to it when an insect brushes past
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wind-pollinated flowers: adaptations
-petals: small and dull-usually green and brown
-nectar: no scent or nectar
-pollen grains: smooth and light so they can easily be carried in the wind and in large amounts to make sure some reach other flowers
-anthers: outside flower, loose on long filaments so that pollen can be released easily
-stigma: outside flower, feather so forms network to catch pollen grains drifting in the wind
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seed and fruit formation:
-pollen grains are the male gamete in plants
-the ovule is the female gamete in plants
1) pollen grains land on stigma (via insect or wind pollination)
2) pollen tube grows out of the pollen grain and down the style into the ovary and then to the ovule
3) the male nucleus travels down the pollen tube from the pollen grain to fuse with the female egg nucleus in the ovule, forming a zygote
4) the zygote undergoes mitosis to form a seed
5) the ovule will become the seed and the ovule wall will become the seed coat
6) the ovary will become the fruit of the plant
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practical: understand the conditions needed for seed germination
-> germination is the process in which seeds begin to develop into a new young plant
-water: needed to activate enzymes to break down the starch food reserves in the seeds
-oxygen: needed for aerobic respiration to release energy for growth
-warmth: optinum temperature for enzymes will increase growth rate
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practical: understand the conditions needed for seed germination- actual practical
method:
1) set up 4 boiling tubes with 10 cress seeds in each, sitting on cotton wool
2) tube a should have dry cotton wool and kept at 20ºC
3) tube b should have moist cotton wool and kept at 20ºC
4) tube c should have boiled water that has been cooled, covered with a layer of oil and kept at 20ºC
5) tube d should have moist cotton wool but is kept at lower temperature (4ºC)
-the results will show that seeds germinate in test tube b only because it has the water, temperature and oxygen required for germination. tube a does not have water, the oil in tube c does not allow for oxygen and tube d is not kept at optimum temperature
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germinating seeds:
-embryo: young root and shoot become the adult plant
-food store: starch for the plant to use until it is able to carry out photosynthesis
-seed coat: a protective covering
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asexual reproduction:
-asexual reproduction produces clones as it only involved on parent, unlike sexual reproduction
natural: runners
-e.g. strawberry plants
-grow horizontally over soil surface and put down roots to form new plants
artificially: cuttings
-tissue samples scraped from parent plant and then placed in agar growth medium with nutrients and auxins
-the sample develop into plantlets and these are planted into compost to grow further
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male reproductive system:
-sex gland: produces semen that contains sperm cells
-sperm duct: sperm passes through this
-testis: contained in scrotum (bag of skin) and produces sperm and testosterone
-penis: passes urine and semen out of the body
-urethra: tube inside the penis to carry urine or semen, a ring of muscle inside stops the two mixing
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female reproductive system:
-ovary: contains ova (female gametes) which develop when FSH is released
-oviduct: connects ovary to the uterus and is lined with ciliated cells that push the ovum towards the uterus for fertilisation
-uterus: has a thick lining so that fertilised eggs can be implanted
-cervix: ring of muscle at lower end of uterus foetus remains in place during pregnancy
-vagina: muscular tube that leads to the inside of the body
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secondary sexual characteristics:
females: oestrogen
-breast development
-menstrual cycle begins
-growth of body hair
-widening of hips
-increased height
males: testosterone
-growth of penis and testes
-production of sperm
-growth of facial and body hair
-muscles development
-voice lowering and breaking
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menstrual cycle:
-the menstrual cycle lasts 28 days and the egg is usually released on day 14 (ovulation)
oestrogen:
-oestrogen causes thickening of the uterus in preparation for implantation of an egg
-levels peak on day 10 and then begin to fall
progesterone:
-progesterone mantains the thick lining of uterus
-inhibits the release of LH and FSH
-the egg matures on day 14 and progesterone starts increasing after this until it reaches its peak 3 days later
-if the egg is not fertlised progesterone levels fall and the uterus lining breaks down in a period that lasts for around 5 days
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developing an embryo:
-the placenta allows diffusion of glucose, oxygen and amino acids from the mother’s blood to the developing foetus for growth
-carbon dioxide and urea from the foetus are passed into the mother’s blood to be removed
-it also takes over the production of progesteron
-amniotic fluid is a liquid contained in a bag (amnion) in the uterus that surrounds the foetus
-it protects the foetus and cushions any rough movement
-when labour begins the amnion breaks and the fluid comes out-often known as a woman’s as a ‘water breaking’
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genetic definitions: gamete, genome, chromosome and gene
-gamete: an organism’s reproductive cell (egg in female and sperm in males), which has half the number of chromosomes (23)
-genome: the entire DNA of an organism
-chromosome: a structure found in the nucleus which is made up of a long strand of DNA
-gene: a short section of DNA that codes for a protein, and therefore contribute to a characteristic
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genetic definitions: alelle/variant, dominant allele and recessive allele
-allele/variant: the different forms of the gene-humans have two alleles for each gene as they inherit one from each parent
-dominant allele: only one (out of the two alleles) is needed for it to be expressed and for the corresponding the phenotype to be observed
-recessive allele: two copies are needed for it to be expressed and for the corresponding the phenotype to be observed
-homozygous: when both inherited alleles
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genetic definitions: homozygous and heterozygus
-homozygous: when both inherited alleles are the same (i.e. two dominant alleles or two recessive alleles)
-heterozygous: when one of the inherited alleles is dominant and the other is recessive
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genetic defitions: genotype and phenotype
-genotype: the combination of alleles an individual has, e.g. Aa
-phenotype: the physical characteristics that are observed in the individual, e.g. eye colour
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punnett square diagrams:
a single gene cross looks at the probability of the offspring of two parents having certain genotypes and phenotypes
-this is done using the alleles the two parents have for a gene and a punnet square diagram
-describes monohybrid inheritance (looking at only one charactersitics, e.g. eye colour)
-however, it is important to remember that most phenotypic features are the result of multiple different genes interacting rather than a single gene inheritance
-uppercase letters are used to represent dominant characteristics
-lowercase letters represent recessive characteristics, letters are usually A or B (can be whatever)
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sex determination:
-human body cells have 23 pairs of chromosomes:
-22 control characteristics, and the chromosomes in each pair look very similar
-the 23rd pair carries sex determining genes, and the two chromosomes can look different to each other (Y chromosomes are much smalles than X chromosome)
-the two possible chromosomes in the 23rd pair are X chromosomes and Y chromosomes
-when cells undergo meiosis to form a gamete, one sex chromosome goes into each gamete
-female have two X chromosomes, so therefore only pass on X chromosomes in their eggs
-males have one X chromosome and one Y chromosome, so therefore can pass on X or Y chromosomes in their sperm
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mitosis:
-> mitosis is a type of cell division where one cell divides to form two identical daughter cells
-the cell cycle is a series of steps that the cell has to undergo in order to do this
-cell division by mitosis occurs during growth and development, replacing damaged cells and also cloning
-mitosis is also a vital part of asexual reproduction, as this type of reproduction only involved one organism so to produce offspring it simply replicates its own cells
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mitosis: method
Stage 1 (interphase):
-the cell grows as organelles (such as ribosome and mitochondria) grow and increase in number
-the synthesis of protein occurs
-all 46 chromosomes are replicated (forming the characteristic ‘X’ shape)
-energy stores are increased
Stage 2:
-the chromosomes line up at the equator of the cell
-spindle fibres pull each chromosome of the ‘X’ to either side (poles) of the cell
Stage 3:
-two identical daughter cells form when the cytoplasm and cell membranes divide, each containing the same 46 chromosomes as the orginal cell
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meiosis:
-> meiosis is the formation of four non-identical cells from one cell
-cells in the reproductive organs divide by meiosis to form gametes
-gametes only have one copy of each chromosome
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meiosis: method
1) the cell makes copies of its chromosomes, so it has double the amount of genetic information
2) the cell divides into two cells, each with half the amount of chromosomes, giving the normal amount of 26 chromosomes (diploid)
3) each cell divides into two again to produce four cells, each with 23 chromosomes. As they have half of the normal amount of chromosomes they are called haploid
-these cells are called gametes and they are all genetically different from each other because the chromosomes are shuffed during the process, resulting in random chromsomes ending up in each of the four cells
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variation:
-genetic variation: is the difference in DNA sequences of individuals within the same species
-random fertilisation: increases genetic variation between offspring as each gamete has variation due to meiosis and the fusing of the egg and sperm is random
-genetic variation: would be eye colour, blood type etc as these phenotypes are dependent on inheriting alleles from parents
-environmental variation: is caused by differences in lifestyle, diet, climate etc. which could lead to organisms to adapt. An examples of this would be how white moths adapted to darker in more polluted areas
-genetics and environment: can interact, such as with height. A child might have the potential to grow tall, due to their genetics, but if they are malnourished and do not well or enough then they will not grow as much
-mutations are rare, random change in genetic material that can be inherited
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Darwin:
-evolution: a change in the inherited charactersitics of a population over time through a process of natural selection which may result in the formation of a new species
-natural selection: the process by which new species arise from existing species
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Darwin: mutations
-mutations occur which provide variation between organisms
-if a mutation provides a survival advantage the organism is more likely to survive to breeding age (survival of the fittest)
-the mutation will then be passed onto offspring
-over many generations, the frequency of the mutation will increase within the population
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Darwin: population
-within a population there is usually a large amount of genetic variation between individuals of the same species
-this natural variation occurs through small mutations that have occurred throughout time
-for example, we can see that within a particular breed of dog there are slightly different coat colours and patternings due to random mutations
-this may cause one population of a species to become so different that they can no longer interbreed to to produce fertile offspring
-this means that they have become a new species, called speciation
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antibiotic resistance in bacteria:
-bacteria are organisms that reproduce at a very fast rate and therefore advantageous genes, such as those for antibiotic resistance, can become prominent within a population very quickly
-exposer to antibiotics creates a selection pressure, as those with antibiotic resistant genes survive and those without die
-as a result those with antibiotic resistance can reproduce and pass on the advantageous gene to their offspring and so the population of antibiotic resistant bacteria increases
-as an examples is the MRSA ‘superbug’ that is resistant to many different types of antibiotics, it is found in hospitals as it spreads when doctors and nurses move between different patients
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definitions: population, community, habitat and ecosystem
-population: all the organisms of one species in a habitat (e.g: a rocky shore or a field)
-community: all the different species in a habitat
-habitat: the place where an organism lives
-ecosystem: all the organisms living in a particular area and all the non-living (abiotic) conditions (e.g: temperature, climate, soil-type)
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practical: investigate the population size of an organism in two different areas using quadrats
-> a quadrat is a square frame enclosing a known area, e.g. 1m^2. To compare the population size of an organism in two sample areas just follow these simple steps:
1) Place a 1 m^2 quadrat on the ground at a random point within the first sample area. You could this by dividing the sample area into a grid and using a random number generator pick to pick coordinates to place your quadrats at. This will help to make sure the results you get are representative of the whole sample area
2) count all the organisms you’re interested in within the quadrat
3) repeat steps 1 and 2 lots of times
4) work out the mean number of organisms per quadrat within the first sample area
5) repeat steps 1 to 4 in the second sample area
6) finally compare the two means
mean = total number of organisms/number of quadrats
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calculations: estimating the population size
1) work out the mean number of organisms per m^2
2) multiply mean per m^2 by the total area (in m^2) of the habitat
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environmental changes:
-the environment in which plants and animals live changes all the time. These changes are caused by abiotic (non-living) or biotic (living) factors and affect communities in different ways- for some species population size may increase, for others it may decrease, or the distribution of populations (where they live) may change
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abiotic factors:
-light intensity: light is required for photosynthesis and the rate of photosynthesis affects the rate at which the plant grows. Also, plants can be food sources or shelter for many organisms
-temperature: temperature affects the rate of photosynthesis
-moisture levels: both plants and animals need water to survive
-soild pH and mineral content: soil pH affects the rate of decay and therefore how fast mineral ions return to soil (which are then taken up by other plants). Different species of plants thrive in different nutrient concentration levels
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biotic factors:
-food availability: more food means organisms can breed more successfully and therefore the population can increase in numbers
-new predators
-new pathogens: when a new pathogen arises the population has no resistance to it so they can be wiped out quickly
-competition: if one species is better adapted to the environment than another, then it will outcompete it until the numbers of the lesser adapted species are insufficient to breed
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feeding relationships: trophic levels
-> trophic levels are the feeding levels in a food chain
-producers: organisms that make their own food by photosynthesis, e.g: plants and algae
-primary consumers: herbivores that only eat plants (producers)
-secondary consumers: carnivores that eat primary consumers
-tertiary consumers: carnivores that eat secondary consumers. They have no predators and so are called the apex predators
-decomposers: bacteria and fungi that break down dead animal’s body and waste for energy, using enzymes
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food chains and food webs:
-food chains: show the feeding relationships between organisms, they are organised by trophic levels
-food webs: are a collection of different food chains to show how all the organisms in the habitat interact showing interpendence
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pyramids of numbers:
-shows the population of each organism at each trophic level of the food chain
-producers are at the bottom and bars usually get smaller the further up you go
-however, if he producer is a large plant, e.g. tree, the size of he bar is very small as one tree can feed many insects (primary consumers)
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pyramids of biomass:
-> pyramids of biomass show the relative biomass at each trophic level of food chain
-it shows the relative dry mass of material at each level
-there is less biomass as you move up the trophic levels
-not all the food consumed by an animal is converted into biomass- this meand the biomass of the organism in the level above another will always be higher, as not all the organism can be consumed and converted into biomass
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energy transfer:
-producers (e.g. plants and algae) transfer about 1% of the incident energy from light for photosynthesis, as not all the ligh lands on the green (photosynthesising) parts of the plant
-only approximately 10% of the biomass of each trophic level is transferred to the next since:
-not all biomass can be eaten -> carnivores cannot generally eat bone, hooves, claws and teeth
-not all of the biomass eaten is converted into biomass of the animal eating it -> lots of glucose is used in respiration, which produces the waste product carbon dioxide + urea is a waste substance which is released in urin + biomass consumed can be lost as faeces-herbivores do not have all the enzymes to digest all the material they eat, so it is egested instead
efficiency of biomass transfer: (biomass transferred to the next level/biomass available at the previous level) x 100
-because less biomass is transferred each time it is common to have a limited number of trophic levels and to find less animals in the higher trophic levels
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the carbon cycle:
-respiration: plants and animals aerobically respire, which releases CO2 into air + decomposers also respire while the break down compounds
-photosynthesis: plants remove CO2 from the air through photosynthesis
-decomposition: dead plants and animals are broken down by decomposers + the carbon is then returned into the atmosphere
-combustion: when plants and fossil fuels (remains of dead animals) are burnt, the carbon dioxide are released into the atmosphere
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sulfur dioxide:
-released when fossil fuels are burnt
-dissolves in water droplets in clouds to form dilute sulfuric acid which creates acid rain
-acid rain makes rivers too acidic, which leads to aquatic organisms dying
-it corrodes metals and limestone in buildings
-it leeches minerals out of soil so plant and trees cannot survive
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carbon monoxide:
-released when fossil fuels are burn through incomplete combustion
-binds irreversibly to haemoglobin, which then reduces the oxygen carrying capacity of red blood cells
-this can lead to tiredness, unscosciuos or even death in severe cases
-in pregnant women, insufficient oxygen affects the growth of the foetus
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effects of global warming:
-climate change
-water levels will rise as glaciers melt from higher temperatures
-loss of habitats
-uninhabitable environments due to climate change means that some species will become extinct or they will migrate to more habitable areas
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greenhouse gases: definition + sources
-greenhouse gases: gases that absorb infrared radiation from the Sun, trapping it above the Earth’s surface (greenhouse effect) which leads to the increase of the Earth’s temperature (global warming)
-water vapour: from rivers, lakes
-carbon dioxide: deforestation, fossil fuels
-nitrous oxide: fertilisers, engines of vehicles
-methane: cattle, rice paddy fields
-CFC (chloroflurocarbons): refrigerators, aerosol sprays
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biological consequences of pollution: pollution of water by sewage
-sewage is rich in minerals and nutrients that will allow decomposers and algae to thrive
-decomposers respire aerobically to break down sewage, which uses oxygen
-sewage may also contain bacteria that also respire aerobically
-the algae bloom stops light from reaching aquatic plants, causing them to die
-these three lead to oxygen depletion, meaning that other aquatic organisms will die
-in sewage treatment works, a lot of oxygen is provided by stirring the waste of injecting jets
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biological consequences of pollution: leached minerals
-eutrophication = when fertilisers are washed off from the land into nearby rivers and lakes by the rain
-the excess nutrients that are washed into the lakes encourages rapid growth of algae
-this algae blocks sunlight reaching the plants below, so they cannot photosynthesis leading to oxygen deprivation
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glasshouses and polyethene tunnels:
-the enclosed environment protects the crops from harsh weather conditions
-carbon dioxide levels, and so therefore rate of photosynthesis
-heat is trapped from the Sun, so the optimum temperature of enzymes can be reached
-the plants are protected from pests that can damage plants or carry diseases
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factors affecting crop yield:
carbon dioxide:
-paraffin lamps can be burned to increase carbon dioxide levels
-this ensures that carbon dioxide is not the limitting factor in the rate of photosynthesis
temperature:
-the heat trapped by the sun in the glasshouse raises the temperature
-this allows the enzymes in photosynthesis to work at the optimum temperature and so the rate of photosynthesis increases
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fertilisers:
-fertilisers contain nutrients that allow plants to grow faster
-these water-soluble minerals can be absorbed into the plant roots by active transport
-nitrates are required to make amino acids for proteins, to allow the plants to grow
-phosphates are required for respiration and root growth
-potassium is needed for growth of flowers and fruit, as it allows enzyme reactions to take place
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pest control + ads & disads:
-> using pesticides or biology control to prevent insects eating the plants, pesticides include fungicides, herbicides and insecticides
advantages:
-quick and efficient
-can kill entire populations
disadvantages:
-organisms can develop resistance
-non-specific so kills other organisms
-bioaccumulation can make it toxic to others in the food chain
-have to continuously apply
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yeast:
-yeast uses anaerobic respiration in order to make bread rise:
glucose —> ethanol + carbon dioxide
C6H12O6 —> ethanol + CO2
-the carbon dioxide bubbles are what causes the bread to rise
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practical: investigate the role of anaerobic respiration by yeast in different conditions
1) dissolve sugar in boiled water
2) mix yeast with sugar solution in a boiling tube
3) add a layer of oil on top in order to prevent oxygen from entering (ensuring that is is only anaerobic respiration taking place)
4) connect the boiling tube to a test tube of lime water
5) count the number of bubbles seen over a set time
-different conditions can be investigated, such as temperature (by using a water bath) or concentration of sugar
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production of yoghurt:
-lactobacillus is a useful bacteria in making yoghurt
-milk contains a sugar called lactose, which lactobacillus can break down to form lactic acid
-this acid lowers the pH of the milk, which denatures proteins to give the yoghurt texture
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the process of making yoghurt:
1) all equipment is sterilised to kill unwanted microorganisms
2) milk is heated to 72ºC for 15 seconds to kill any microorganisms in the milk-this is called pasteurisation
3) the milk is cooled and lactobacillus is added
4) the mixture is incubated at around 40ºC in a fermenter-here the bacteria breaks down lactose to lactic acid
5) the thickened yoghurt is produced and any flavouring, colorants or fruit are added before packaging
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industrial fermenter:
-fermenters are containers that grow bacteria and fungi in large amounts, this can be useful when producing transgenic bacteria for example:
-aseptic conditions are required to ensure that no other microorganism grows and contaminates the containers
-nutrients are needed for the microorganism to use in respiration
-optimum temperature and pH are needed in order for enzymes to work at the high rate but are not denatured
-agitation by stirring paddles is required to ensure that the nutrients, oxygen, temperature, pH and microorganisms are distributed evenly
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selective breeding + process:
-> is when humans choose which organisms to breed in order to produce offspring with a certain desirable characteristic (e.g. animals with more meat, plants with disease resistance or big flowers)
-this has been happening for many years since animals were domesticated and plants were grown for food
1) parents with desired characteristics are chosen
2) they are bred together
3) from the offspring those with desired characteristics are bred together
4) the process is repeated many times until all the offspring have the desired characteristic
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inbreeding:
-breeding can lead to inbreeding
-breeding those with similar desirable characteristics means it is likely you are breeding closely related individuals
-this results in the reduction of the gene pool, as the number of different alleles reduce (as they mostly have the same alleles)
-this means if the environment changes or there is a new disease, the species could become extinct as they have the same genetic make-up (so the chance of a few organisms having a survival advantage and not dying is reduced)
-another problem is that the small gene pool leads to a greater chance of genetic defects being present in offspring, as recessive characteristics are more likely to be present
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genetic engineering:
-> modifrying the genome of an organism by introducing a gene from another organism to give a desired characteristic
-plant cells have been engineered for disease resistance or to have larger fruits
-bacterial cells have been engineered to produce substances useful to humans, such as human insulin to treat diabetes
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restriction enzymes:
-> enzymes which are able to cut DNA at specific sites, leaving ‘sticky ends’ (short sections of exposed, unpaired bases)
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ligase enzymes:
-enzymes that are used to join pieces of DNA together
-the virus or plasmid DNA is then cut using the same restriction enzyme and the desired gene is placed inside and then joined by ligase enzymes
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the process of human insulin production:
1. the insuline gene for a healthy individual is ‘cut out’ using restriction enzymes leaving ‘sticky ends’
2. a virus or bacterial plasmid is cut using the same restriction enzyme to also create sticky ends
3. the sticky ends from the virus or plasmid and the sticky ends from the genes are then joined together by ligase enzymes
4. the combined loop is placed in a vector, such as a bacterial cell, and then allowed to mutiply as it will now contain the modified gene
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genetic modified crops:
-they are engineered to be resistant to insects and herbicides
-this will result in increades yields as less crops will die
-transgenic: transfer of genetic material from one species to a different species
