Hard Stuff Flashcards
1
Q
What parts do animal cells have?
A
- Nucleus.
- Cytoplasm.
- Cell Membrane.
- Mitochondria.
- Ribosomes.
2
Q
What parts do plant cells have?
A
- Nucleus.
- Cytoplasm.
- Cell membrane.
- Mitochondria.
- Ribosomes.
- Rigid cell wall.
- Permanent vacuole.
- Chloroplasts.
3
Q
What does the nucleus do in a cell?
A
-Contains genetic material that controls the activities of the cell.
4
Q
What does the Cytoplasm do in the cell?
A
-Gel-like substance where most of the chemical reactions happen. It contains enzymes that control these chemical reactions.
5
Q
What does the Cell membrane do in the cell?
A
-Holds the cell together and controls what goes in and out.
6
Q
What do the Mitochondria do in the cell?
A
-These are where most of the reactions for respiration take place. Respiration releases energy that the cell needs to work.
7
Q
What do Ribosomes do in the cell?
A
-These are where proteins are made in the cell.
8
Q
What does the rigid cell wall do in the cell?
A
-Made of cellulose. It supports the cell and strengthens it.
9
Q
What does the permanent vacuole do in the cell?
A
-Contains cell sap, a weak solution of sugar and salts.
10
Q
What do chloroplasts do in the cell?
A
-These are where photosynthesis occurs, which makes food for the plant. They contain a green substance called chlorophyll.
11
Q
What is yeast and what does it contain in its cell?
A
- Yeast is a single-called microorganism.
- It has a nucleus, cytoplasm, and a cell membrane surrounded by a cell wall.
12
Q
What is Bacteria and what does its cell contain?
A
- Bacteria is a single-celled microorganism.
- A Bacteria has a cytoplasm and a cell membrane surrounded by a cell wall.
- The genetic material floats in the cytoplasm because bacterial cells don’t have a nucleus.
13
Q
What is the definition for diffusion?
A
-Diffusion is the spreading out of particles from an are of high concentration ton an area of low concentration.
14
Q
What states does diffusion happen in?
A
-Solutions and gases - that’s because the particles in these substances are free to move about randomly.
15
Q
What happens to the rate of diffusion when the the difference in concentration increases?
A
-The bigger the difference in concentration, the faster the diffusion rate.
16
Q
How do dissolved substances move in and out of cells?
A
-Dissolved substances can move in and out of cells by diffusion.
17
Q
How do cell membranes help diffusion?
A
- Only very small molecules can diffuse through cell membranes - things like oxygen (needed for respiration) glucose, amino acids and water.
- Big molecules like starch and proteins can’t fit through the membrane.
18
Q
Which way do particles flow in diffusion?
A
-They’re only moving about randomly, so they go both ways - but if there are a lot more particles on o e side of the membrane, there’s a net (overall) movement from that side.
19
Q
How are Palisade Leaf Cells adapted for Photosynthesis? (4 points).
A
- Packed with chloroplasts for photosynthesis. More of them are crammed at the top of the cell - so they’re nearer the light.
- Tall shape means a lot of surface area exposed down the side for absorbing CO2 from the air in the leaf.
- Thin shape means that you can pack loads of them in at the top of a leaf.
- Palisade leaf cells are grouped together at the the top of the leaf where most of the photosynthesis happens.
20
Q
What are Guard Cells adapted to doing?
A
-Opening and Closing Pores.
21
Q
What are Palisade Leaf Cells adapted to doing?
A
-Photosynthesis.
22
Q
How are Guard Cells adapted to allowing gas exchange and controlling water loss within a leaf? (5 points).
A
- Special kidney shape which opens and closes the stomata (pores) in a leaf.
- When plants have lots of water, guard cells fill up with it - go plump and turgid. Makes stomata open so gases can be exchanged for photosynthesis.
- When plant is short of water, guard cells lose water - become flaccid, making stomata close. Helps stop too much water vapour escaping.
- Thin outer walls and thickened inner walls make opening and closing work.
- Also sensitive to light and close at night to save water without losing out on photosynthesis.
23
Q
What are Red Blood Cells adapted to do?
A
-Carry oxygen.
24
Q
How are red blood cells adapted to carry oxygen? (4 points).
A
- Concave shape gives a big surface area for absorbing oxygen. Also helps them pass smoothly through capillaries to reach body cells.
- Packed with haemoglobin - the pigment that absorbs oxygen.
- Have no nucleus, to leave even more room for haemoglobin.
- Red blood cells = an important part of the cell.
25
What are sperm and egg cells specialised to do?
-Reproduction.
26
How are egg cells adapted for reproduction? (4 points).
- The main functions of an egg cell are to carry the female DNA and to nourish the developing embryo in the early stages.
- The egg cell contains huge food reserves to feed the embryo.
- When a sperm fuses with the egg, the egg's membrane instantly changes its structure to stop any more sperm getting in. This makes sure the offspring end up with the right amount of DNA.
- Sperm and egg cells are very important cells in reproduction.
27
How are sperm cells adapted for reproduction? (6 points).
- The function of a sperm is basically to get the male DNA to the female DNA.
- It has a long tail to help it swim to the egg.
- It has a streamlined head to help it swim to the egg.
- There are a lot of mitochondria in the cell to provide the energy needed.
- Sperm also carry enzymes in their heads to digest the egg cell membrane.
- Sperm and egg cells are very important cells in reproduction.
28
How do cells become specialised for a particular job?
-Differentiation.
29
When does differentiation occur?
-Differentiation occurs during the development of a multicellular organism.
30
What are similar cells organised into?
-Similar cells are organised into tissues. A tissue is a group of cells that work together to carry out a particular function.
31
What are three examples of tissues and what they do?
- Muscular tissue, which contracts (shortens) to move whatever it's attached to.
- Glandular tissue, which makes and secretes chemicals like enzymes and hormones.
- Epithelial tissue, which covers some parts of the body, e.g. the inside of the gut.
32
What are tissues organised into?
-Tissues are organised into Organs. An organ is a group of different tissues that work together to perform a certain function.
33
What are examples of tissues that the stomach (organ) is made up of?
- Muscular tissue, which moves the stomach wall to churn up the food.
- Glandular tissue, which makes the digestive juices to digest food.
- Epithelial tissue, which covers the outside and the inside of the stomach.
34
What are the organs organised into?
-Organs are organised into Organ Systems. An organ system is a group of organs working together to perform a particular function.
35
What organs are in the digestive system (found in humans and mammals) which breaks down food?
- Glands (e.g. the pancreas and salivary glands) which produce digestive juices.
- The stomach and small intestine, which digest food.
- The liver, which produces bile.
- The small intestine, which absorbs soluble food molecules.
- The large intestine, which absorbs water from undigested food, leaving faeces.
36
What organs are plants made up of?
- Stems.
- Roots.
- Leaves.
37
What tissues are leaves made up of and what do they do?
- Mesophyll tissue - this is where most of the photosynthesis in a plant occurs.
- Xylem and phloem - they transport things like water, mineral ions and sucrose around the plant.
- Epidermal tissue - this covers the whole plant.
38
What is the equation for photosynthesis?
-Carbon dioxide + water >(sunlight and chlorophyll.)> glucose + oxygen.
39
What does photosynthesis produce?
- Glucose - 'food'.
| - Oxygen.
40
Where does photosynthesis occur in a plant cell?
-Photosynthesis happens inside the chloroplasts.
41
How does photosynthesis occur in the chloroplasts?
-Chloroplasts contain a green substance called chlorophyll, which absorbs sunlight and uses its energy to convert carbon dioxide (from the air) and water (from the soil) into glucose. Oxygen is produced as a by-product.
42
What type of plants does photosynthesis occur in?
-Photosynthesis happens in the leaves of all green plants - this is largely what the leaves are for.
43
What factors can become the limiting factor in the rate of photosynthesis?
- Light.
- Temperature.
- CO2.
44
What are some examples of the environmental conditions affecting which factor is the limiting factor?
- At night light is the limiting factor.
- In winter it's often the temperature that is the limiting factor.
- If it's warm enough and bright enough, the amount of CO2 is usually the limiting factor.
45
What is an easy experiment to work out the ideal conditions for photosynthesis in a particular plant?
- Easiest type is to use a water plant like Canadian pondweed - you can easily measure the amount of oxygen produced in a given time to show how fast photosynthesis (oxygen is produced in photosynthesis).
- You could either count the bubbles given off, or if you want to be a bit more accurate you could collect the oxygen in a gas syringe.
46
How does light affect the rate of photosynthesis?
-Light provides the energy needed for photosynthesis.
-As the light level is raised, the rate of photosynthesis increases steadily - but only up to a certain point.
-Beyond that, it won't make any difference because then it'll be either the temperature or the
CO2 level which is the limiting factor.
47
How does the amount of CO2 affect the rate of photosynthesis?
- CO2 is one of the raw materials needed for photosynthesis.
- As with light intensity the amount of C02 will only increase the rate of photosynthesis up to a point. After this the graph flattens out showing that CO2 is no longer the limiting factor.
48
What is one way to control the amount of CO2?
-Dissolve different amounts of sodium hydrogencarbonate in the water, which gives off CO2.
49
What effect does temperature have on the rate of photosynthesis?
- Usually if temperature is the limiting factor, it is because the temperature is too low - the enzymes needed for photosynthesis work more slowly at low temperatures.
- But if the plant gets too hot, the enzymes it needs for photosynthesis and it's other reactions will be damaged.
- This happens at about 45degrees (which is pretty hot for outdoors, although greenhouses an get that hot sometimes).
50
What is the best way to control the temperature of the flask?
-Put the flask in a water bath.
51
How can you artificially create the ideal conditions for farming?
- Most common way to artificially create the ideal environment for plants is to grow them in a greenhouse.
- Greenhouses help trap the sun's heat - make sure temperature doesn't become the limiting factor. In winter - farmer may use heater. In summer - temperature could get too hot, so they may use shades and ventilation to cool things down.
- Commercial farmers often supply artificial light after the Sun goes down to give their plants more quality photosynthesis time.
- Farmers and gardeners can also increase the level of carbon dioxide in the greenhouse. A fairly common way is to use a paraffin heater to hear the greenhouse. As the paraffin burns, it makes carbon dioxide as a by-product.
- Keeping plants enclosed in a greenhouse makes it easier to keep them free from pests and diseases. Farmer can add fertilisers as well, to provide all the minerals needed for healthy growth.
- All this costs money - but if farmer can keep the conditions just right for photosynthesis, the plants will grow much more often, which can then be sold. It's important that a farmer supplies just the right amount of heat, light, etc - enough to make the plants grow well, but not more than the plants need, as this would just be wasting money.
52
What are the 5 ways plants use glucose?
- For Respiration. This releases energy which enables them to convert the rest of the glucose into various other useful substances, which they can use to build new cells and grow. To produce some of these substances they also need to gather a few minerals from the soil.
- Making Cell Walls. Glucose is combed into cellulose for making strong cell walls, especially in a rapidly growing plant.
- Making Proteins. Glucose is combined with nitrate ions (absorbed from the soil) to make amino acids, which are then made into proteins.
- Stored in Seeds. Glucose is turned into lipids (fats and oils) for storing in seeds. Sunflower seeds, for example, contain a lot of oil - we get cooking oil and margarine from them. Seeds also store starch.
- Stored as Starch. Glucose is turned into starch and stored in roots, stems and leaves, ready for use when photosynthesis isn't happening, like in the winter. Starch is insoluble which makes it better for storing than glucose - a cell with lots of glucose in would draw in loads of water and swell up. Potato and parsnip plants store a lot of starch underground over the winter so a new plant can grow from it the following spring. We eat the swollen storage organs.
53
What is the distribution of the organism?
-Where an organism is found, e.g. in a part of the playing field.
54
What environmental factors affect where an organism is found (the distribution of an organism)?
- Temperature.
- Availability of water.
- Availability of oxygen and carbon dioxide.
- Availability of nutrients.
- Availability of light.
55
Why might an organism be more common in one area than another?
-Due to differences in environmental factors between the two areas. For example, in a field, you might find that daisies are more common in the open, than under trees, because there's more light available in the open.
56
What are two ways to study the distribution of an organism?
- You can measure how common an organism is in two sample areas (e.g. using quadrats) and compare them.
- You can study how the distribution changes across an area, e.g. by placing quadrats along a transect.
57
How do you set up comparing the population of an organism in two sample areas?
- Place a 1 m^2 quadrat on ground a random point.
- Count all organisms within the quadrat.
- Repeat steps 1-2 many times as possible.
- Wprk out mean number of organisms per quadrat within the first sample are.
- Repeat steps 1-4 in second sample area.
- Finally compare the two means.
58
How do you work out the population size of an organism in one sample area?
- Work out the mean number of organisms per m^2 (same as mean for 1m^2 quadrat result).
- Then multiply the mean by the total area (in m^2) of the habitat.
59
How do you use transacts to study the distribution of organisms along a line?
- Mark out a line in the area you want to study using a tape measure.
- Then collect data along the line.
- You can do this by just counting all the organisms you're interested in that touch line.
- Or, you can collect data using quadrats. These can be placed next to each other along the line or at intervals, for example, every 2m.
60
How do you make your results reliable when collecting environmental data?
- Quadrats and transect are pretty good tools for finding out how an organism is distributed.
- But, you have to work hard to make sure your results are reliable - means making sure they are repeatable and reproducible.
- To make them more reliable, need to use a larger sample size. Bigger sample sizes = more representative of the whole population, so results using a larger sample are more likely to be reproducible.
61
How do you make your results valid when collecting environmental data?
- For results to be valid they must be reliable and answer the original question.
- To answer original question, need to control all the variables.
- The question you need to answer is whether a difference in distribution between two sample areas is due to a difference in distribution is caused by the environmental factor or not.
- If you don't control the other variables you won't know whether any correlation you've found is be chase of chance, because of the environmental factor you're looking at or because of a different variable - study won't give you valid data.
- Another way to improve validity of your results is to use random samples. If samples are all in one spot, and everywhere else is different, the results you get won't be valid.
62
What do enzymes act as?
-Biological catalysts.
63
What do enzymes do?
-They reduce the need for high temperatures and we only have enzymes to speed up the useful chemical reactions in the body.
64
What is the definition for a catalyst?
-A catalyst is a substance which increases the speed of a reaction, without being changed or used up in the reaction.
65
What type of substance are all enzymes?
-Proteins and all proteins are made up of chains of amino acids. These chains are folded into unique shapes, which enzymes need to do their jobs.
66
As well as catalysts what do proteins act as?
-Proteins act as structural components of tissues (e.g. muscles), hormones and antibodies.
67
Why must an enzyme have a special shape?
- Every enzyme has a unique shape that fits into the substance involved in a reaction.
- Enzymes are picky - usually only catalyse one reaction.
- Because, for an enzyme to work, the substance has to fit it's special shape. If the substance doesn't match the enzyme's shape, then the reaction won't be catalysed.
68
Why do enzymes need the right temperature and pH?
- Changing the temperature changes the rate of an enzyme-catalysed reaction.
- Like with any reaction, a higher temperature increases the rate at first. But if it gets too hot, some of the bonds holding the enzyme together break. This destroys the enzyme's special shape and so it won't work any more. It's said to be denatured.
- The pH also affects enzymes. If it's too high or too low, the pH interferes with the bonds holding the enzyme together. This changes the shape and denatures the enzyme.
- All enzymes have an optimum pH they work best at.
69
What temperature do enzymes in the body generally work best at?
-Enzymes in the human body normally work best at around 37degrees.
70
What is the optimum pH of most enzymes in the human body?
-Often neutral pH7.
71
What is the other optimum pH for enzymes and where is this?
-Pepsin is an enzyme used to break down proteins in the stomach. It works best at pH 2 which means it's well-suited to the acidic conditions there.
72
What do the digestive enzymes do?
-Break down the big molecules into the smaller ones.
73
What does amylase do?
Breaks starch down into Maltose and other sugars, e.g. dextrins.
74
Where is amylase produced?
- Amylase is made in three places:
- The salivary glands.
- The pancreas.
- The small intestine.
75
What does protease do?
-Converts proteins into amino acids.
76
Where is protease made?
- Protease is made in three places:
- The stomach. (it's called pepsin there).
- The pancreas.
- The small intestine.
77
What does lipase do?
-Converts lipids into glycerol and fatty acids.
78
Where is lipase made?
- Lipase is made in two places:
- The pancreas.
- The small intestine.
79
Where is bile produced?
-Bile is produced in the liver.
80
Where is bile stored and released?
-It's stored in the gall bladder before it's released into the small intestine.
81
What does bile do and why?
- The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly. Bile is alkaline - it neutralises the acid and makes conditions alkaline. The enzymes in the small intestine work best in these alkaline conditions.
- It emulsifies fats. In other words it breaks the fat into tiny droplets. This gives a much bigger surface area of fat for the enzyme lipase to work on - which makes its digestion faster.
82
What do the salivary glands do in the digestive system?
-These produce amylase enzyme in the saliva.
83
What does the liver do in the digestive system?
-It is where bile is produced. Bile neutralises stomach acid and emulsifies fats.
84
What does the gall bladder do in the digestive system?
-It is where bile is stored, before it's released into the small intestine.
85
What does the stomach do in the digestive system?
- It pummels the food with its muscular walls.
- It produces the protease enzyme, pepsin.
- It produces hydrochloric acid for two reasons:
- To kill bacteria.
- To give the right pH for the protease enzyme to work. (ph 2 - acidic).
86
What does the pancreas do in the digestive system?
-Produces protease, amylase and lipase enzymes. It releases these into the small intestine.
87
What does the small intestine do in the digestive system?
- Produces protease, amylase and lipase enzymes to complete digestion.
- This is also where the digested food is absorbed out of the digestive system into the blood.
88
What does the large intestine do in the digestive system?
-It is where excess water is absorbed from the food.
89
What does the rectum do in the digestive system?
-It is where the faeces (made up mainly of indigestible food) are stored before they exit through the anus.
90
What is the definition for respiration?
-Respiration is the process of releasing energy from glucose, which goes on in every cell.
91
What is the word equation for aerobic respiration?
-Glucose + oxygen > carbon dioxide + water + energy.
92
What does aerobic respiration happen in all the time?
- Plants.
| - Animals.
93
What do most of the aerobic respirations reactions happen in?
-Most of the reactions in aerobic respiration happen inside mitochondria.
94
What four things does respiration release energy for?
- To build up larger molecules from smaller ones (like proteins from amino acids).
- In animals, to allow the muscles to contract (allows them to move about).
- In mammals and birds the energy is used to keep their body temperature steady (unlike other animals, mammals and birds keep their bodies constantly warm).
- In plants, to build sugars, nitrates and other nutrients into amino acids, which are then built up into proteins.
95
What does physical activity do to you?
- Increases your breathing rate and makes you breathe more deeply to meet the demand for extra oxygen.
- Increases the speed at which the heart pumps.
96
What happens to an unfit person compared to a fit person during and after exercise?
-An unfit person's heart rate goes up a lot more during exercise than a fit person, and they take longer to recover.
97
How do muscles work during exercise?
- Muscles are made of muscle cells. These use oxygen to release energy from glucose (aerobic respiration), which is used to contract the muscles.
- An increase in muscle activity requires more glucose and oxygen to be supplied to the muscle cells. Extra carbon dioxide needs to be removed from the muscle cells. For this to happen the blood has to flow at a faster rate.
98
How is glycogen used during exercise?
- Some glucose from food is stored as glycogen.
- Glycogen's mainly stored in the liver, but each muscle has its own store.
- During vigorous exercise muscles use glucose rapidly, so some of the stored glycogen is converted back to glucose to provide more energy.
99
When is anaerobic respiration used?
- Anaerobic respiration is used if there's not enough oxygen.
- "Anaerobic" just means "without oxygen". It's the incomplete breakdown of glucose, which produces lactic acid.
100
What is the word equation for anaerobic respiration?
-glucose > energy + lactic acid.
101
Why is anaerobic respiration not the best way to convert glucose into energy?
- It is not the best way to convert glucose into energy because lactic acid builds up in the muscles, which gets painful. It also causes muscle fatigue - the muscles get tired and then stop contracting efficiently.
- Another downside is that anaerobic respiration does not release nearly as much energy as aerobic respiration - but it's useful in emergencies.
102
What is the advantage to anaerobic respiration?
-The advantage is that at least you can keep on using your muscles for a while longer.
103
What does anaerobic respiration lead to?
- Oxygen debt.
- You have to "repay" the oxygen that you didn't get to your muscles in time, because your lungs, heart and blood couldn't keep up with the demand earlier on.
- This means you have to keep breathing hard for a while after you stop, to get more oxygen into your blood. Blood flows through your muscles to remove the lactic acid by oxidising it to harmless CO2 and water.
- While high levels of CO2 and lactic acid are detected in the blood (by the brain), the pulse and breathing rate stay high to try and rectify the situation.
104
What are enzymes used for?
- Biological detergents.
- Mainly protein-digesting enzymes (professes) and fat-digesting enzymes (lipase).
- Because the enzymes break down animal and plant matter, they're ideal for removing stains like food or blood.
- Biological detergents are also more effective at working low temperatures (e.g. 30degrees) than other types of detergents.
105
What are enzymes used to do in food?
- Enzymes are used to change foods.
- The proteins in some baby foods are 'pre-digested' using protein-digesting enzymes (proteases), so they're easier for the baby to digest.
- Carbohydrate-digesting enzymes (carbohydrases) can be used to turn starch syrup into sugar syrup which is a lot nicer tasting.
- Glucose syrup can be turned into fructose syrup using an isomerase enzyme. Fructose is sweeter, so you can use less of it - good for slimming foods and drinks.
106
What are advantages to using enzymes in industry?
- They're specific, so they only catalyse the reaction you want them to.
- Using lower temperatures and pressures means a lower cost as it saves energy.
- Enzymes work for a long time, so after the initial cost of buying them, you can continually use them.
- They are biodegradable and therefore cause less environmental pollution.
107
What are the disadvantages to using enzymes in the industry?
- Some people can develop allergies to the enzymes (e.g. in biological washing powders).
- Enzymes can be denatured by even a small increase in temperature. They're also susceptible to poisons and changes in pH. This means the conditions in which they work must be tightly controlled.
- Enzymes can be expensive to produce.
- Contamination of the enzyme with other substances can affect the reaction.
108
What does DNA stand for?
-Deoxyribonucleic acid.
109
What and is DNA and where is it found?
- It contains all the instructions to put an organism together and make it work.
- It's found in the nucleus of animal and plant cells, in really long molecules called chromosomes.
110
What does a gene code?
- A gene codes for a specific protein.
- A gene is a section of DNA. It contains the information to make a specific protein.
- Genes simply tell cells in what order to put the amino acids together.
- DNA also determines what proteins the cell produces, e.g. haemoglobin, keratin.
- Then in turn determines what type of cell it is, e.g. red blood cell, skin cell.
111
What is everyone's DNA?
-Everyone has unique DNA. The only exceptions are identical twins, where the two people have identical DNA, and clones.
112
What is DNA fingerprinting?
-DNA fingerprinting (or genetic fingerprinting) is a way of cutting up a person's DNA into small sections and then separating them. Every person's genetic fingerprint has a unique pattern (unless they're identical twins or clones). This means you can tell people apart by comparing samples of their DNA.
113
What is DNA fingerprinting used in?
- Forensic science - DNA (from hair, skin flakes, blood, semen etc.) taken from a crime scene is compared with a DNA sample taken from a suspect.
- Paternity testing - to see if a man is the father of a particular child.
114
What are the advantages/disadvantages with having a national genetic database of everyone in the country?
- (Advantage) That way, DNA from a crime scene could be checked against everyone in the country to see whose it was.
- (Disadvantage) But others think this is a big invasion of privacy, and they worry about how safe the data would be and what else it might be used for.
- (Disadvantage) There are also scientific problems - false positives can occur if errors are made in the procedure or if the data is misinterpreted.
115
What is mitosis used for?
- Mitosis males new cells for growth and repair.
- When a body cell divides it needs to make new cells identical to the original cell - with the same number of chromosomes.
- This type of cell division is called mitosis. It's used when plants and animals want to grow or to replace cells that have been damaged.
116
What is the definition for mitosis?
-"Mitosis is when a cell reproduces itself by splitting to form two identical offspring."
117
List the steps of mitosis.
- In a cell that's not dividing, the DNA is all spread out in long strings.
- If the cell gets a signal to divide, it needs to duplicate its DNA - so there's one copy for each new cell. The DNA is copied and forms X-shaped chromosomes. Each 'arm' of the chromosome is an exact duplicate of the other.
- The chromosomes then line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell.
- Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells.
- Lastly, the cytoplasm divides.
- You now have two new cells containing exactly the same DNA - they're identical.
118
What other function uses mitosis in the body?
- Asexual reproduction also uses mitosis.
- Some organisms also reproduce by mitosis, e.g. strawberry plants form runners in this way, which become new plants.
- This is an example of asexual reproduction.
- The offspring have exactly the same genes as the parent - so there's no variation.
119
How many chromosomes do body cells normally have?
-Body cells normally have two copies of each chromosome - one from the organism's 'mother' and one from it's 'father'. So humans have 23 pairs of chromosomes in our body cells so 46 chromosomes in total.
120
How many chromosomes do gametes have?
- Gametes have one copy of each chromosome. This is so that you can combine one sex cell from the 'mother' and one sex cell from the 'father' and still end up with the right number of chromosomes in body cells.
- The gametes have 23 chromosomes each, so that when an egg and sperm (gametes) combine, you get 46 chromosomes again (23 pairs of chromosomes).
121
What is an example of when meiosis is used?
- Sexual reproduction.
- The new individual will have a mixture of two sets of chromosomes, so it will inherit features from both parents. This is how sexual reproduction produces variation.
122
Where does meiosis only happen?
-In humans, it only happens in the reproductive organs. As to make new cells which only half the original number of chromosomes, cells divide by meiosis.
123
What is the definition of meiosis?
-"Meiosis produces cells which have half the normal number of chromosome."
124
List the steps of meiosis.
- As with mitosis, before the cell starts to divide, it duplicates its DNA - one arm of each chromosome is an exact copy of the other arm.
- In the first division in meiosis (there are two divisions) the chromosome pairs line up in the centre of the cell.
- The pairs are then pulled apart, so each new cell only has one copy of each chromosome. Some of the father's chromosomes and some of the mother's chromosomes go into each new cell.
- In the second division the chromosomes line up again in the centre of the cell. It's a lot like mitosis. The arms of the chromosomes are pulled apart.
- You get four gametes each with only a single set of chromosomes in it.
- After two gametes join at fertilisation, the cell grows by repeatedly dividing by mitosis.
125
In animals when is the ability to differentiate lost?
-At an early stage.
126
In plants when is the ability to differentiate lost?
-Lots of plant cells don't ever lose this ability.
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What are stem cells?
-Undifferentiated cells that can develop into different types of cells depending on what instructions they're given.
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Where are stem cells found?
- Stem cells are found in early human embryos. Makes sense - all the different types of cell found in a human being have to come from those few cells in the early embryo.
- Adults also have stem cells, but they're only found in certain places, like bone marrow. These aren't as versatile as embryonic stem cells - they can't turn into any cell type at all, only certain ones.
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What are the arguments for stem cells?
- Stem Cells may be able to cure many diseases. Medicine already uses adult stem cells to cure disease. For example, people with some blood diseases (e.g. sick cell anaemia) can be treated by bone marrow transplants. Bone marrow contains stem cells - can turn into new blood cells - replace faulty old ones.
- Scientists can also extract stem cells from very early human embryos and grow them.
- These embryonic stem cells could be used to replace faulty cells in sick people - you could make beating heart muscle cells for people with heart disease, insulin-producing cells for people with diabetes, nerve cells for people paralysed by spinal injuries, and so on.
- To get cultures of one specific type of cell, researchers try to control the differentiation of the stem cells by changing the environment they're growing in. So far, it's still a bit hit and miss - lots more research is needed.
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What are the arguments for and against stem cell research?
- They feel that human embryos shouldn't be used for experiments since each one is a potential human life.
- Others think curing a patients who already exist and who are suffering is more important than the rights of embryos.
- Embryos used in research are usually unwanted ones from fertility clinics which, if they weren't used for research, would probably just be destroyed. However, campaigners for rights of embryos also want this banned too.
- Campaigners think scientists should concentrate on finding and developing other sources of stem cells, so people could be helped without having to use embryos.
- In some countries stem cell research is banned, but it's allowed in the UK as long as it follows strict guidelines.
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What are the 23rd pair of chromosomes labelled?
-XX or XY.
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What chromosome pair do men have?
-All men have an X and a Y chromosome. XY. The Y chromosome causes male characteristics.
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What chromosome pair do women have?
-All women have two X chromosomes. XX. The XX combination allows female characteristics to develop.
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When making sperm what are the chances of getting a Y-chromosome and an X-chromosome and when making an egg what are the chances of getting an X-chromosome?
- When making sperm, the X and Y chromosomes are drawn apart in the first division of meiosis. There's a 50% chance each sperm cell gets an X-chromosome and a 50% chance it gets a Y-chromosome.
- A similar thing happens when making eggs. But the original cell has two X-chromosomes, so all the eggs have one X-chromosome.
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How do you work out the probability of getting a boy or a girl?
- To find the probability of getting a boy or a girl, you can draw a genetic diagram.
- Genetic Diagrams show the possible combinations of Gametes.
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Who was Gregor Mendel?
- Gregor Mendel was an Austrian monk who trained in mathematics and natural history at the University of Vienna.
- On his garden plot at the monastery, Mendel noted how characteristics in plants were passed on from one generation to the next.
- The results of his research were published in 186) and eventually became the foundation of modern genetics.
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What did Mendel do that was different to before?
-He did a first generation of breeding, but then he also crossbreed two of the offspring in the first generation in his second generation to show how characteristics can change.
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What did Mendel show?
- The height characteristic in pea plants was determined by separately inherited "hereditary units" passed on from each parent.
- The ratios of tall and dwarf plants in the offspring showed that the unit for tall plants, T, WA dominant over the unit for dwarf plants, t.
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What are the three important conclusions that Mendel reached about heredity in plants?
- Characteristics in plants are determined by "hereditary units".
- Hereditary units are passed on from both parents, one unit from each parent.
- Hereditary units can be dominant or recessive - if an individual has both the dominant and the recessive unit for a characteristic, the dominant characteristic will be expressed.
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Why was the significance of Mendel's work only realised after his death?
-Because in Mendel's time, nobody knew anything about genes or DNA ("hereditary units" are genes), and so the significance of his work was not to be realised until after his death.
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What are alleles?
-Different versions of the same gene.
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What does homozygous mean?
-When an organism has two alleles for a particular which are the same.
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What does heterozygous mean?
-When its (an organism's) two alleles for a particular gene are different.
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What are dominant and recessive alleles and how are they shown?
- If the two alleles are different,money one can determine what characteristic is present.
- The allele for the characteristic that's shown is called the dominant allele - use a capital letter for dominant alleles - e.g. 'C'.
- The other one is called recessive - use a small letter for recessive alleles - e.g. 'c'.
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How must an organism show a recessive characteristic?
-For an organism to display a recessive characteristic, both its alleles must be recessive - e.g. cc.
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How must an organism show a dominant characteristic?
-For an organism to display a dominant characteristic the organism can be either CC or Cc, because the dominant allele overrules the recessive one if the plant/animal/other organism is heterozygous.
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What does genotype mean?
-Genotype means what alleles you have - e.g. 'cc and CC'.
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What does phenotype mean?
-Phenotype means the actual characteristic.
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What is cystic fibrosis caused by?
- The recessive allele.
- 'f'.
- Carried by about 1 person in 25.
- Because it's recessive, people with only one copy of the allele won't have the disorder - they're known as carriers.
- For a child to have the disorder, both parents must be either carriers or sufferers.
- 1 in 4 chance if both parents are carriers.
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What is polydactyly caused by?
- The dominant allele.
- Can be inherited if just one parent carries the defective allele.
- The parent that has the defective allele will be a sufferer too since the allele is dominant.
- There's a 50% chance of a child having the disorder if one parent has the D (dominant) allele.
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What does embryonic screening help do?
- During IVF, before the embryos are implanted, it's possible to remove a cell from each embryo and analyse its genes.
- Many genetic disorders could be detected in this way, such as cystic fibrosis.
- Embryos with 'good' alleles would be implanted into the mother - the ones with 'bad' alleles destroyed.
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What are the arguments against embryonic screening?
- There may come a point where everyone wants to screen their embryos so they can pick the most 'desirable' one, e.g. they want a blue-eyed, blond-haired, intelligent boy.
- The rejected embryos are destroyed - they could have developed into humans.
- It implies that people with genetic problems are 'undesirable' - this could increase prejudice.
- Screening is expensive.
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What are the arguments for embryonic screening?
- It will help to stop people suffering.
- There are laws to stop it going too far. At the moment parents cannot even select the sex of their baby (unless it's for health reasons).
- During IVF, most of the embryos are destroyed anyway - screening just allows the selected one to be healthy.
- Treating disorders costs the Government (and the taxpayers) a lot of money.
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How are fossils made from gradual replacement by minerals?
- Most fossils happen this way.
- Things like teeth, shells, bones etc., which don't decay easily, can last a long time when buried.
- They're eventually replaced by minerals as they decay, forming a rock-like substance shaped like the original hard part.
- The surrounding sediments also turn to rock, but the fossil stays distinct inside the rock and eventually someone digs it up.
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How are fossils formed from casts and impressions?
- Sometimes, fossils are formed when an organism is buried in a soft material like clay. The clay later hardens around it and the organism decays, leaving a cast of itself. An animal's burrow or a plant's roots can be preserved as casts.
- Things like footprints can be pressed into these materials when soft, leaving an impression when it hardens.
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How are fossils made from preservation in places where no decay happens?
- In amber (a clear yellow 'stone' made from fossilised resin) and tar pits there's no oxygen or moisture so decay microbes can't survive.
- In glaciers it's too cold for the decay microbes to work.
- Peat bogs are too acidic for decay microbes.
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What are some ideas about how life began?
- A primordial swamp (or under the sea) here on Earth.
- Simple organic molecules were brought to Earth by comets - these could have the become more complex organisms, and eventually very simple life forms.
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Why is there lack of evidence to hypotheses suggesting how life first came into being?
- Many early organisms were soft-bodied, and soft tissue tends to decay away completely. So the fossil record is incomplete.
- Plus fossils that did form millions of years ago may have been destroyed by geological activity, e.g. the movement of tectonic plates may have crushed fossils already formed in the rock.
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What are the reasons why a species become extinct?
- The environment changes too quickly (e.g. destruction of habitat).
- A new predator kills them all.
- They can't compete with another (new) species for food.
- A catastrophic event happens that kills them all (e.g. a volcanic eruption or a collision with an asteroid).
- A new species develops (this is called speciation).
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What is the definition for a species?
-A species is a group of similar organisms that can reproduce to give fertile offspring (must say "can reproduce to give fertile offspring" in the exam to get full marks I think).
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What is speciation?
-The development of a new species.
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When does speciation occur?
-Speciation occurs when populations of the same species become so different that they can no longer breed together to produce fertile offspring.
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What is isolation and how does it happen?
- Isolation is where populations of a species are separated.
- This can happen due to a physical barrier. E.g. floods and earthquakes can cause barriers that geographically isolate some individuals from the main populations.
- Conditions on either side of the barrier will be slightly different, e.g. they may have different climates.
- Because the environment is different on each side, different characteristics will become more common in each population due to natural selection.
- Eventually, individuals from the different populations will have changed so much that they won't be able to breed with one another to produce fertile offspring.
- The two groups will have become separate species.
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What is natural selection?
- Each population shows variation because they have a wide range of alleles.
- In each population, individuals with characteristics that make them better adapted to their environment have a better chance of survival and so are more likely to breed successfully.
- So the alleles that control the beneficial characteristics are more likely to be passed on to the next generation.
