Flashcards in Biology 2 Deck (200):
What happens in light microscopes?
-In light microscopes, light passes through a specimen and then though magnifying lenses so you see the object much bigger than it really is. The best modern light microscopes can magnify specimens more than 1500 times.
What are microscopes used for?
-Microscopes are used to learn about the structure and the function of cells, of which organisms are made.
What are the parts of animal cells?
What does the cell membrane do?
-The cell membrane separates the contents of the cell and its surroundings. It controls the movement of substances like oxygen, glucose and carbon dioxide into and out of the cell.
What does the cytoplasm do?
-The cytoplasm is where many of the chemical reactions needed to carry out life processes take place. It also contains organelles, which are tiny structures that carry out specific jobs.
What does the nucleus do?
-The Nucleus is an organelle that contains DNA, which is the genetic material. The nucleus also controls all the activities of the cell.
What does the mitochondria do?
-Mitochondria are organelles in which respiration occurs (oxygen and glucose react to release energy needed by the cell). They are very tiny and cannot been seen easily through a light microscope at low magnification.
What do the ribosomes do?
-Ribosomes are organelles in which protein synthesis occurs.
What are the parts of plant cells?
-Chloroplasts (containing chlorophyll)
What does the cell wall do?
-The cell wall is made of tough cellulose to support the cell and allow it to keep its shape.
What does the vacuole do?
-The vacuole is a large space in the cytoplasm that is filled with cell sap and helps to support the plant by keeping the cells rigid.
What do the chloroplasts do?
-Chloroplasts are organelles that contain chlorophyll, a green substance that absorbs light energy used in photosynthesis.
What are the parts of bacteria cells?
-Flagellum (not always present)
What does the chromosomal DNA do?
-Chromosomal DNA is a giant loop of DNA containing most of the genetic material. It is not neatly packaged like human or plant DNA.
What does the plasmid DNA do?
-Plasmid DNA are small loops that carry extra genetic information.
What does the flagellum do?
-The flagellum is not present in all bacteria cells. It is a long whip-like structure that bacteria can use to move themselves along.
What happens in electron microscopes?
-In the early 1930's the electron microscope was invented. This uses a beam of electrons to magnify specimens up to about 2,000,000 times. Electron microscopes produce very clear images and have helped us to discover much more about the detailed structure of cells.
-For example, electron microscopes show us that bacteria does not have a nucleus, but two types of DNA.
-It also shows us that the bacteria cell wall is different to a plant cell wall. It does a similar job but is more flexible and not made of cellulose.
What are chromosomes?
-The chromosomes in the nuclei of your cells contain your genetic information. They are made of a chemical called DNA.
What are genes?
-Genes are sections of DNA and contain information for specific proteins that are used in your body.
-One gene contains the instructions for one protein. Often several genes work together to produce what is needed for a single feature. Some genes also carry the instructions for the proteins that control the chemical processes in your body.
How is DNA structured?
-There are two strands in a molecule of DNA (deoxyribonucleic acid) that are coiled together to form a spiral known as the double helix. The two strands, made of sugar (deoxyribose) and phosphate, are linked together at regular intervals by chemicals called bases.
How do DNA bases pair up?
-The bases always pair up in the same way because of the complementary (matching) shape of the molecules.
-The matching base pair are known as complementary base pairs and are joined together by weak hydrogen bonds. The order of the bases in DNA contains the information needed to form the proteins for body cells. We each have a slightly different order of bases in our genes and this makes us all slightly different, however 99.9% of DNA is identical to others).
What DNA bases are paired together?
-Adenine (A) pairs with thymine (T)
-Cytosine (C) pairs with guanine (G)
Who discovered the structure of DNA?
-Maurice Wilkins and Rosalind Franklin, in London.
-James Watson and Francis Crick, in Cambridge.
What role did Wilkins and Franklin play in the discovery of DNA?
-In London in the 1950's, Maurice Wilkins and Rosalind Franklin were studying the structure of DNA using X-rays. Franklin directed beams of X-rays at purified DNA and used photos to record how the molecule shattered the X-rays. From the patterns she could work out how the groups of atoms in the DNA molecule were arranged.
What role did Watson and Crick play in the discovery of DNA?
-In Cambridge, James Watson and Francis Crick were trying to build a 3D molecular model of DNA using data from a number of other scientists. They used X-ray results from the London team including some of Franklin's best X-ray images that Wilkins had shown them without Franklin's permission. It was the detail in her images that gave Watson and Crick the clues they needed to build their double helix model.
What is the Human Genome Project (1990-2003)?
-The Human Genome Project (HGP) was an international effort that involved scientists working in 18 different countries and sharing the data they collected using the latest IT to help them.
-In 2003, after 13 years of work, the HGP was complete. Scientists had worked out the sequence of the 3 billion base pairs that make up the human genome. Although each human being has a unique DNA sequence, the project shows that everyone has at least 99.9% of their DNA in common.
Knowing the sequence of the human genome has many implications for science and medicine. What is it being used to develop?
-Improved testing for genetic disorders, to discover if people are carrying a faulty allele.
-New ways of finding genes that may increase the risk of certain diseases, e.g. Alzheimer's, heart disease.
-New treatments and cures for disorders, e.g. gene therapy, where scientists try to replace or mend faulty genes that cause the disorder.
-New ways of looking at changes in the genome over time - this shows us how humans have evolved and the evolutionary relationships between different species.
-Personalised medicines - these are medicines that work with a particular genotype and target diseases more effectively, with fewer side effects.
What is genetic engineering?
-Genetic engineering is the process in which scientists can remove a gene from one organism and insert it into the DNA of another organism. Organisms that have been modified are known as genetically modified organisms (GMOs).
What is an example of genetic engineering?
-Scientists have inserted the gene for human insulin into bacterial plasmid DNA. The genetically modified (GM) bacteria can then make human insulin, which is used by people with diabetes.
What are the advantages and disadvantages of the production of human insulin using GM bacteria?
-Insulin used to be extracted from dead cattle and pigs but insulin from GM bacteria can now be used by vegans.
-It means that the supply of insulin is not affected by animal diseases or the number of animals slaughtered for meat.
-Using bacteria in fermenters, insulin can be made in vast quantities and can be made more cheaply.
-Bacteria might produce the insulin slightly differently.
-There are minute differences and it might not suit everyone.
How are rice plants genetically modified?
-Golden rice plants are normal rice plants that have had two extra genes inserted so that they make beta-carotene in the grains. Beta-carotene is needed by humans to produce vitamin A. A lack of vitamin A can cause death because the immune system does not work properly. It can also cause blindness.
What are the advantages and disadvantages of the production of beta-carotene in rice plants using genetic engineering?
-Without beta-carotene, humans can't produce vitamin A, which could cause death and blindness, due to the immune system not working properly.
-Some people are concerned that the GM rice will crossbreed with wild rice plants and contaminate the wild rice DNA.
-Others believe that eating GM organisms might harm people although there is no evidence for this).
-Some people say that the levels of beta-carotene in golden rice are not high enough to make much difference to children's health.
-GMOs can also be expensive to buy and some are made so that they do not produce fertile seed (meaning farmer have to buy new seed each year).
How are some plants genetically modified?
-Scientists have added genes to some plants to make them herbicide resistant.
What are the advantages and disadvantages of making some plants herbicide resistant using genetic engineering?
-It can reduce the amount of crop spraying needed because the farmer can use one much heavier spray of herbicide rather than several smaller doses.
-The development of herbicide-resistant weeds as cross-pollination with wild rice plants take place.
-Loss of biodiversity as fewer weeds survive.
-Loss of food and shelter for animals.
What are diploid cells?
-Most of the cells in your body contain a nucleus, and most nuclei contain two copies of each chromosome. This makes them diploid cells.
-Human diploid cells contain two sets of 23 chromosomes. Body cells (all cells except sperm and egg cells) are diploid.
What is mitosis?
-To make more body cells, during growth or to replace damaged cells, body cells divide using a process called mitosis. This process begins with the chromosomes making copies of themselves in a process called DNA replication. The copies of the chromosomes separate and then cell then divides. This produces two daughter calls, which are genetically identical to each other and to the parent cell.
-Replication of cells (cell division)
What reproduction process is mitosis involved in?
-Mitosis can produce new, complete individuals in a process called asexual reproduction. Bacteria cells often do this by splitting in half. Some plants reproduce asexually by making new plantlets attached to the parent plant, which then split off to grow on their own.
What is sexual reproduction?
-In many organisms a process called sexual reproduction produces new individuals. This requires two sex cells or gametes. These are different to body cells in that they only have one set of chromosomes, s these are haploid cells. The two gametes fuse during fertilisation and produce a diploid cell called a zygote. The zygote develops into a ball of cells (an embryo).
What is meiosis?
-A different kind of cell division called meiosis is needed to produce haploid gametes. Meiosis also starts with DNA replication, but this is then followed by two cell divisions. The first separates the two sets of chromosomes and the second separates the copies of each chromosome. This produces four haploid daughter cells, each containing one set of chromosomes.
What does a diploid cell contain?
-In a diploid cell, each chromosome in a pair contains the same genes but may have different versions of those genes (alleles). So the chromosomes in a pair are slightly different. In meiosis, these slightly different chromosomes are split between the daughter cells in a random way to produce gametes that are genetically different from each other.
What are the differences between mitosis and meiosis?
-used for growth and repair of cells
-used in asexual reproduction
-cells with identical number of chromosomes and genetic information are produced, 'clones'
-used to produce haploid gametes for sexual reproduction
-each daughter cell have half the number of chromosomes of the parent
What are clones?
-Clones are individuals that are genetically identical.
How can plants be cloned?
-Making pant clones can be easy - you can start with a bit of leaf, stem or root from the original plant. The plant cells divide and produce new cells, which grow into a clone of the original plant. This is an example of asexual reproduction.
Why is it harder to clone animals than plants?
-It is much more difficult to clone animals than plants, because it is not possible to make a whole new animal from an arm or leg. The fist clone produced in a lab of a vertebrate was a frog and was made in 1952. However, the first cloned large animal (a sheep called Dolly) wasn't produced until 1996 because of difficulties with the process.
What was the drawbacks with Dolly the sheep, and therefore with large cloned animals?
-Very few embryos produced during animal cloning develop successfully. Dolly was the only lamb produced after 237 cloning attempts. Dolly also seemed to grow older much more quickly than normal and died young. Scientists aren't sure if her health problems were caused by being a clone or by chance.
Why is cloning useful?
-Cloning is useful to make a genetically identical copy of an adult organism that has desirable characteristics. For example, bulls whose sperm produces high quality calves are valuable and so worth cloning.
-Cloning is also used to produce copies of individuals with a genetically engineered trait, such as cows engineered to produce human insulin in their milk, because this will guarantee that all the offspring will have the engineered trait.
How can a mammal be cloned?
-There are different ways of producing cloned animals, but currently the most successful method uses a process called nuclear transfer. The nucleus of a body cell of the animal to be cloned is transferred into an enucleated egg cell (one that has had its original nucleus removed). The cell is then stimulated with an electrical current to start mitotic division, to form an embryo. This is implanted into the uterus (womb) of a surrogate mother who is a different individual to the parent. Here it will develop and grow into a new individual.
-The first kitten to be produced by nuclear transfer was CC (Copycat) was born on 22 December 2001.
Why is there a lot of interest in human embryos?
-There is a lot of interest in human embryos because when they are a few days old the cells in them are embryonic stem cells.
-In most countries, trying to produce clones humans is illegal. However, in the UK scientists can produce cloned human embryos for research but these embryos must be killed after 14 days.
What happens when a stem cell divides?
-When a stem cell divides it can produce more stem cells or it can produce other types of cells that are specialised or differentiated (e.g neurones, muscle cells, skin cells).
Why are people more interested in embryonic stem cells rather than adult stem cells?
-Once a cell has differentiated it cannot turn into another type of cell. Stem cells in differentiated body tissues (adult stem cells) can only differentiate into a few types of cell. However, embryonic stem cells can develop into every type of human cell. This means that these cells could be used to solve many more problems than adult stem cells could. However, this technique could also be used illegally by people like Dr Zavos to produce human clones.
How are embryonic stem cells sourced?
-One way of collecting embryonic stem cells is to use leftover embryos created for couples having fertility treatment. However, when the embryonic stem cells are extracted, the embryo is killed, so this procedure is controversial. That's why scientists are interested in using adult cells to make cloned embryos.
What are stem cell treatments used for?
-Since the 1960s, adult stem cells from bone marrow have been used to treat leukaemia (a cancer of certain white blood cells). The patient's white blood cells are destroyed and adult stem cells from someone else are put into the patient. These cells then multiply and produce new, healthy white blood cells. This is known as a bone marrow transplant. The treatment does not always work because the body destroys cells from other people if they are too different.
How can the problem with bone marrow transplants be solved?
-The problem with bone marrow transplants may be solved using cloning. If a cloned embryo is created using a skin cell from a person with leukaemia, the embryonic stem cells can be taken and used to produce the cells that make white blood cells. These will survive inside the patient because their body will recognise them as their own cells.
How are scientists trying to solve the problem of using embryonic stem cells?
-Scientists have started to investigate ways of turning differentiated body cells into stem cells by reprogramming them. If this works, it will help avid the ethical problem of using embryos. But further research is needed to make any treatment with stem cells safe because if they are injected into a body they may produce he wrong kind of cell or even create cancer cells.
What do the order of bases on a DNA strand form?
-The order of bases on a DNA strand forms the genetic code. These are only four bases (adenine, A; cytosine, C; guanine, G; thymine, T) but they can be arranged in any sequence, e.g. ATTAGCG.
How many amino acids in human proteins are there?
-There are 20 different amino acids in human proteins.
What does a cell use the sequence of bases for?
-A cell uses the sequence of bases in DNA to synthesise (build) chains of these amino acids. These chains then form proteins. This process is called protein synthesis.
How is each amino acid identified?
-Each amino acid is identified by a different group of bases. A specific order of bases in DNA produces a specific order of amino acids in the chain and so produces a particular protein.
What is the first stage of protein manufacture?
-The first stage of the process is transcription, which takes place inside the nucleus. Here, the DNA in a gene unzips by breaking the weak hydrogen bonds between bases in the double helix. One strand of the gene is used as a template. Bases that are complementary to this strand link together opposite it, forming a molecule of messenger RNA (mRNA). mRNA is small enough to move out of the nucleus into the cell's cytoplasm.
What is mRNA?
-RNA is very similar to DNA but only has one strand (not two) and has a base called uracil (U) instead of thymine.
What is the second stage of protein manufacture?
-In the cytoplasm, the mRNA attaches to a small structure called a ribosome. The ribosome moves from one end of the mRNA strand to the other, decoding the bases in groups of three, known as base triplets or codons. Each amino acid is attached to a transfer RNA (tRNA) molecule, and each tRNA molecule has a triplet of bases. The triplet of bases controls which amino acid is attached.
-As the ribosome moves to the next codon on the mRNA, the tRNA with complementary bases lines up with the codon. The tRNA releases the amino acid that it was carrying which joins on to the growing amino acid chain. The tRNA is released as the ribosome moves onto the next codon, where the next tRNA with its amino acid lines up. This continues until the mRNA strand is completely decoded. The chain of amino acids is called a polypeptide. The polypeptide then twists and fold and may link up with other polypeptides, to become a protein.
What is the number and order of amino acids specific for?
-The number and order of the amino acids in the chain is specific for each protein.
-The protein insulin, which helps cells take in glucose, has a small chain of 51 amino acids in an order that no other protein has.
-Haemoglobin is a much larger, complex protein found in red blood cells. It carries oxygen and is made of four linked chains, two of which have 141 amino acids and two have 146 amino acids.
What does the order of amino acids cause the chain to do?
-The order of the amino acids causes the chain to fold up in a particular way and gives the protein a specific 3D shape.
-Some proteins such as keratin found in human hair and nails, for long, strong fibrous molecules.
-Other proteins such as insulin, haemoglobin and enzymes, have a round 'globular' (blobby) shape.
Why is the shape of enzymes particularly important in the way they work?
-Each enzyme has a unique shape caused by its amino acid sequence. An enzyme can only work in one kind of reaction because of its shape. We say that each enzyme is specific to the reaction.
What is a mutation?
-A mutation is a change in the sequence of bases in the genetic code. Some changes in the code have no effect on the amino acid sequence produced, so the protein shape is not affected.
-Mutations may be harmful or may have no effect, and some can be beneficial to the organism. For example, some mutations in bacteria make them resistant to the effects of antibiotics. Bacteria that have the mutation survive when that antibiotic is used, but bacteria without the mutation die.
What happens in the sickle-cell mutation?
-The sickle-cell mutation in the gene that produces haemoglobin, replace one amino acid in the chain with another. This can cause the protein to fold up in a different way and have a different shape, which will affect the way it works.
What is a point mutation?
-A change in a single base pair.
What is a gross mutation?
-A change in large chunks of base pairs. The may have been flipped, in the wrong place or missing altogether,
What are the main causes of mutation?
-During reproduction, DNA doesn't replicate properly.
-Environmental, radiation and toxic compounds.
What are enzymes?
-There are thousands of chemical reactions going on in the body at the same time. To work well and quickly, each reaction is controlled by one particular group of proteins called enzymes. Without enzymes, these reactions might still happen but at too sow a rate for cells to so all they need to stay alive.
What is a catalyst?
-A substance that helps a chemical reaction go faster without itself being changed by the reaction is called a catalyst.
-An enzyme is a biological catalyst.
What is an example of enzymes working inside cells?
-During DNA replication in mitosis, or meiosis, the DNA double helix is unwound and the weak hydrogen bonds separating the two strands are separated by one particular enzyme (rather like unzipping a zip). As the new bases line up along each half, so that the complementary base pairs match, a different enzyme joins them together. This make two complete and identical DNA molecules. The enzymes are unchanged so they can repeat their action wherever it is needed in the DNA.
How do enzymes play a part in protein synthesis?
-During protein synthesis, when a protein s built from amino acids using the order of bases in the DNA code as a guide, there are many different reactions. Each of these reactions is catalysed by a different enzyme. For example, as a protein is built the reaction that joins one amino acid to another is catalysed by a specific enzymes.
What is an example of enzymes working outside cells?
-Food molecules, such as carbohydrates, proteins and fats, are much too large to pass across the cell membranes of the gut wall and into the blood. They need to be broken down first in a process called digestion. Different enzymes are released into the mouth, stomach and small intestine to help digest different food molecules into smaller ones that can be absorbed into the cells.
-Microorganisms and fungi also release digestive enzymes, but because they don't have a gut, the grow one and through the food they are digesting. After the enzymes have digested the food, the small molecules are absorbed through the microorganisms's cell walls. Some of these enzymes are now used in laundry detergents to help digest food an other large molecules that stain clothes.
What are substrate molecules?
-The molecules that enzymes work on are called substrate molecules. Enzymes catalyse the change of substrate molecules into product molecules better at some temperatures than others, so the rate of reaction is faster.
How do enzymes work best?
-At temperatures much above or below an optimum value, enzymes don't work as well. This is partly why the processes in your body don't work as well when you have a fever, because if the temperature is too high, the enzymes denature.
-Enzymes also often work best at an optimum pH. Most enzymes in cells work best about pH 7, but enzymes in the digestive system have to work well at a much higher or lower pHs.
-The rate of reaction catalysed by an enzyme will also increase as the concentration of substrate increases but only up to a point. Beyond that concentration, there is no further change in reaction rate. This is because the enzyme cannot work on the substrate any faster than at this rate. So adding more substrate molecules will make no difference to the rate.
What is a key feature of enzymes?
-A key feature of enzymes is that each enzyme will only work with a particular substrate, or small group of similar substrates. We say that they are highly specific for the substrate. This feature is used to name enzymes. For example;
-carbohydrases catalyse the breakdown of carbohydrates
-proteases catalyse the breakdown of proteins
Why is the shape important in enzyme action?
-All the substrate molecules for one particular enzyme have the same 3D shape in some part of their molecules.
-Looking at the 3D shapes of enzymes and their substrates shows that the substrate fits neatly into an active site in the enzyme. The active site has a different shape in different enzymes. Since the shape of their substrate fits tightly into the hole of the active site, the model of how enzymes work is called the 'lock-and-key' hypothesis.
What happens to emzymes when the pH or temperature changes?
-Changing the pH or temperature a little changes the shape of the active site so the substrate does not fit as well. Too much change will break the bonds within the enzyme. This can change the shape so much that it denatures the enzyme and destroys the active site.
What is an example of a larger molecule being broken down into a smaller one by an enzyme?
-Digestion; when amylase breaks down starch into glucose.
What is an example of a larger molecule being formed from a smaller one by an enzyme?
-Protein synthesis; when amino acids are joined together to make a protein.
In cells, what is energy needed for?
-All organisms are made of cells and energy is needed to power the many processes a cell carries out. This energy is released in a series of enzyme-catalysed reactions known collectively as respiration.
What is respiration?
-Respiration is the release if energy from food molecules that acts as fuel for the cell.
Why do cells that are more active need more energy?
-Cells that are more active have higher energy requirements. During exercise the muscles contract to cause movement, and this requires a great deal of energy from respiration. Growing and dividing cells also need lots of energy to power the building of new cell materials.
What happens in aerobic respiration?
-In aerobic respiration, oxygen is used to release energy from molecules such as glucose. The glucose and oxygen are converted into carbon dioxide and water and energy is released for use in the cell (mitochondria-organelle energy is used).
What is the equation for aerobic respiration?
-glucose + oxygen --> carbon dioxide + water + energy from glucose, released for use in the cell.
-C6H12O6 + O2 --> CO2 + H2O
What is diffusion?
-Diffusion occurs when particles of a substance spread out, moving from an area where they are in a higher concentration to an area where they are in lower concentration. The particles diffuse down a concentration gradient.
Why does diffusion occur when respiring?
-In humans, the glucose and oxygen needed for respiration are carried around the body and into tissues by blood. As well as carrying glucose and oxygen, blood must also carry waste carbon dioxide away from respiring cells. All these substances move between respiring cells and tiny blood vessels called capillaries by a process called diffusion.
What happens to gas levels in cells during respiration?
-In respiring cells, oxygen and glucose levels fall as they are used up in aerobic respiration. At the same time, carbon dioxide levels in the cells rise.
What is gas exchange?
-Lung tissue is spongy and full of tiny air sacs (alveoli). These sacs are surrounded by capillaries, and oxygen that enters the body through the lungs moves into the blood by diffusion. Carbon dioxide also leaves the blood by diffusion into the air spaces. As one gas is entering the bloodstream another one is leaving it; this is called gas exchange.
What happens during gas exchange in the lungs?
-Blood enters from the rest of the body with a higher concentration of carbon dioxide and a lower concentration of oxygen. Blood flows through the capillaries, which have a thin wall, so carbon dioxide can diffuse through the thin capillary and thin alveolus wall, and then out of the lungs and oxygen can diffuse into the blood passing through the capillaries. The alveolus has a higher concentration of oxygen and a lower concentration of carbon dioxide, and then eventually the blood goes to the rest of the body with a lower concentration of carbon dioxide and a higher concentration of oxygen.
What is a pulse?
-Your pulse is a way of measuring your heart rate. Your pulse is a surge of blood in your arteries as your heart pumps blood around your body, so by counting you pulse you can measure the number of times your heart beats.
What happens to oxygen and glucose during exercise?
-The more active a cell is the more energy it needs so respiration must happen at an increased rate. During exercise, the muscles use up oxygen and glucose very quickly, so the blood supply to the muscles must increase.
What does the amount of blood circulated by the heart depend on?
-The amount of blood circulated by the heart depends not only on the heart rate, but also the stroke volume.
What is stroke volume?
-Stroke volume is the volume of blood pumped out of the heart on each beat.
What is cardiac output?
-Cardiac output is the volume of blood circulated y the heart in a given time.
What is the equation to measure cardiac output?
-Cardiac output = stroke volume x heart rate.
Why does cardiac output increase with exercise?
-Heart rate and stroke volume increase with exercise, so cardiac output also increases. This delivers more blood to respiring tissues faster.
Why does our breathing rate increase when we exercise?
-Extra blood is of limited use to the respiring tissues if it doesn't contain enough oxygen. To make sure it does, our breathing rate increases to increase the rate of oxygen uptake in the lungs.
Why does anaerobic respiration occur?
-When we carry out intense exercise, we cannot supply oxygen to out muscles quickly enough. When this happens an alternative process to break down glucose and release energy that does not rely on oxygen starts to occur alongside aerobic respiration. It is called anaerobic respiration.
What happens in anaerobic respiration?
Anaerobic respiration releases less energy than aerobic respiration. Lactic acid is broken down, using oxygen, into carbon dioxide and water. After exercise increased oxygen is required to break down lactic acid and to release energy for other processes in cells (for example, cell repair).
What is the equation for anaerobic respiration?
-glucose --> lactic acid + energy from the glucose, released for use in the cell.
What can a build up of lactic acid cause?
What is the requirement for additional oxygen after exercise called?
-The requirement for additional oxygen after exercise is called excess post-exercise oxygen consumption (EPOC). This used to be called the 'oxygen debt'.
How can additional oxygen after exercise be obtained?
-Extra oxygen, needed after exercise, can be obtained and distributed by maintaining a high breathing rate and a high heart rate which is one of the reasons why they remain relatively high for a few minutes after exercise.
What is recovery time?
-The time taken for the pulse rate to return to the normal or resting rate after exercise is the recovery time.
What are the effects of a reduced cardiac output?
-Less blood flow, so less blood leaving the heart.
-Less oxygen and glucose reach muscles, so there is a reduced rate of aerobic respiration, and less energy is released and less carbon dioxide removed. There is a greater rare of anaerobic respiration, meaning glucose is broken down without oxygen, so there is reduced muscle contraction and a build up of lactic acid causing cramps and fatigue.
How is starch made and broken down?
-Starch is made by joining together thousands of glucose molecules. When starch is broken down in digestion, glucose is released and can be used for respiration.
Why do plants need a supply of glucose?
-Plant cells also need to respire so needs a supply of glucose.
How do plants manufacture their own glucose?
-Plants can manufacture their own glucose using the simple raw materials of carbon dioxide and water. This process is called photosynthesis. Plants can also store the glucose they make as carbohydrates, like starch.
What is the equation for photosynthesis?
-carbon dioxide + water + energy from sunlight --> glucose + oxygen
-CO2 + H2O --> C6H12O6 + O2
-6CO2 + 6H2O --> C6H12O6 + 6O2 (balanced)
Where does photosynthesis take place?
-Photosynthesis is a complex series of enzyme-catalysed reactions which occurs inside cell organelles called chloroplasts.
What is the energy source for photosynthesis?
-Light is the energy source for photosynthesis and is absorbed by a green substance inside chloroplasts called chlorophyll.
Why is chlorophyll important in photosynthesis?
-Without chlorophyll, photosynthesis cannot occur. Chlorophyll transfers the light energy into the stored chemical energy in glucose.
In what ways have leaves adapted for photosynthesis?
-The leaf is the main organ in which photosynthesis occurs. Leaves have several adaptations for photosynthesis, including;
-The presence of chloroplasts containing chlorophyll to absorb light energy.
-Leaves are broad and flat to provide a very large surface area which helps them absorb as much light energy as possible.
What is the Stomata, and what part does it play in photosynthesis?
-On the underside of a leaf there are microscopic pores called stomata. The stomata open in response to light. These pores allow carbon dioxide in the atmosphere to diffuse into the leaf, to be taken up by photosynthesising cells. Oxygen produced by these cells can also diffuse from the inside of the leaf out to the atmosphere. Plant cells produce water in respiration, some of which evaporates from their surfaces and diffuses out of the leaf.
Why are the air spaces inside the leaf needed?
-The air spaces inside the leaf give the cells a large surface area to volume ration for efficient gas exchange.
How is plant growth maximised?
-To maximise plant growth, the rate of photosynthesis must be maximised as the glucose made in photosynthesis is used to make proteins for growth as well as respiration.
What must there be, in order for photosynthesis to take place?
-For photosynthesis to take place, there must be a supply of;
-a suitable temperature
-light to provide energy for the reactions to occur.
What is a limiting factor?
-A single factor that when in short supply can limit the rate of a process such as photosynthesis.
-For example; A plant growth in dim light with ample carbon dioxide and water will photosynthesis slowly. Increasing the amount of carbon dioxide or water will not increase the rate of photosynthesis. Only increasing the amount of light will increase the rate. In this case, light is the limiting factor.
How are processes affected by the limiting factor?
-In any process that is affected by several factors, the maximum rate at which the process can occur is controlled by the factor that is in shortest supply, that factor is the limiting factor.
What is the effect of light intensity on the rate of photosynthesis in a plant (other variables kept constant)?
-Initially, an increase in light intensity causes and increase in the rate of photosynthesis. The plant can photosynthesise faster if it is given more light and so light intensity is the limiting factor in these conditions.
-Eventually, the rate of photosynthesis becomes constant, even though more light energy is available. One possibility is that carbon dioxide concentration is now the limiting factor. Another limiting factor could be temperature. The enzymes involved in photosynthesis are working as fast as they can but raising the temperature would allow the rate to increase further.
What is the job of roots, apart from anchoring the plant into the ground?
-Roots do more than just anchor the plant into the ground - they take up water and mineral salts from the soil. The surface of the roots have specialised root hair cells with long thin extensions that reach into the surrounding soil. The root hairs provide a large surface area for substances to enter the root.
What is osmosis?
-Water enters the root hair cells by osmosis. In this process, water moves across a partially permeable membrane (a membrane that only certain substances can pass through) from a region where water is in higher concentration to a region where it is in lower concentration. This is the same as diffusion. Osmosis is also a form of passive transport because it does not require any energy from the plant at all.
What is active transport?
-Roots can absorb nitrate and other mineral ions dissolved in soil water even if their concentration is higher in the plant than in the soil water. Absorbing particles against a concentration gradient is called active transport. The energy needed for this process comes from respiration.
What specialised tissue do plants have?
-Once water and minerals have entered the root cells, they need to get up to all the plant's tissues.
-Xylem is a specialised tissue to transport water and dissolved mineral salts. Xylem tissue consists of long cells that die and form hollow tubes. These tubes also give support to the plant.
-Phloem is strands of living tissue, that transports the glucose, made in leaves by photosynthesis which is converted to sucrose, to other parts of the plant.
What is transpiration?
-Water that evaporates from the surface of cells inside a leaf moves out of the leaf by diffusion when the stomata is open. This maintains a concentration gradient, so more water evaporates and diffused out of the leaf. The loss of water from the leaf pulls water and dissolved mineral salts up through the xylem from the roots. This process is called transpiration. Factor that increase evaporation will also increase transpiration.
What is a potometer?
-A potometer can be used to monitor transpiration. As the stem taken up water, the air bubble moves along the capillary tube.
What do the conditions in an environment determine?
-The conditions in an environment determine which organisms (plants, animals and microorganisms) can survive in it.
-The icy conditions of the Arctic and the humid heat of the rainforest each present challenges for living organisms. They must be adapted to their environments and be able to respond to any changes.
What is the study of biodiversity?
-Ecologists study the biodiversity of life found in an ecosystem or habitat, where a particular organism is found (its distribution), as well as how many individuals there are in a group of the same species (the population size). These data are used to monitor changes in population size or distribution or to test a hypotheses about what sort of organisms exist in a certain place.
What is sampling?
-Sampling means looking at a small portion of an area or population. In random sampling, every point within an area has an equal chance of being selected. This means the sample is likely to be representative of the whole area.
What techniques are used for sampling?
-A pooter is used to catch small invertebrates through an inlet tube by sucking sharply on a second tube connected to the container
-In areas with long grass, a sweep net can be used to catch some of the organisms present.
-A pond net can be used to sample aquatic habitats.
-Pitfall traps are useful for trapping small animals such as spiders, beetles, and woodlice. They can be set up and left overnight so it is possible to catch organisms that might not be active during the day.
What are quadrats?
-Quadrats are square frames of known size, which are typically used to sample the number and population of different plant species in a habitat. The quadrat is placed at random locations, for example by throwing, and the number of plants of each type that appear within the quadrat are counted. For spreading plants like clover the percentage of the quadrat area that is covered by the plant is estimated.
What is random sampling used for?
-Random sampling is used to estimate a total population size by scaling up the mean number of one type of plant per quadrat.
What can you learn about organisms, considering the varying conditions in a habitat?
-By considering the varying conditions in a habitat, such as at different points in a field, it is possible to understand why the organisms that live there are able to do so.
-For example, understanding how light intensity varies might help to explain the distribution of different species of plants. Other factors such as temperature, soil or water pH may also have an effect in determining which organisms can survive in any given part if a habitat.
What is systematic sampling?
-When investigating changes in a habitat caused by one environmental factor it is sometimes useful to carry out systematic sampling along a line.
-For example, quadrats could be placed at regular intervals along a straight line.
What are fossils?
-Fossils are the preserved traces of remains of organisms that lived thousands or millions of years ago. We find fossils when the rocks containing them are weathered.
What is the fossil record?
-The history of life on Earth as shown by fossils from periods of time is known as the fossil record. This suggests that organisms have changed gradually through time (a process called evolution).
Why does the fossil record have gaps in it?
-The fossil record has many gaps in it. Soft tissues decay and do not usually form fossils, so soft-bodied organisms leave little fossil evidence behind. -Other dead organisms did not form fossils because the hard parts were destroyed.
-Many fossils are buried deep in the earth and have not yet been found.
Why do scientists have to interpret how organisms changed over time?
-The gaps is the fossil record mean that scientists must interpret how organisms changed over time from incomplete data. The same sets of fossil data can be interpreted in different ways, often because fossils are frequently damages or incomplete. The scientists who first found Megalosaurus fossils thought it had a huge head and walked on four legs. They hadn't found all the bones. Better fossil evidence shows it was a small, headed dinosaur walking on two legs.
Why is it important to collect more fossil evidence?
-The more fossil evidence we can collect, the better conclusions we can draw. We can date fossils accurately now and use computers to model how the organism might have looked.
What evidence do we have to show the evolution of vertebrates?
-Most vertebrates have limbs, and though the limb may look very different on the outside, the internal bone structure is very similar. This is also true of fossil vertebrates. Even fossil ancestors of limbless living vertebrates have the same basic five-fingered (pentadactyl) limb structure.
-This suggests that all vertebrates evolved from one common ancestor hundreds of millions of years ago. Looking at the fossil record, scientists can explain the evolution of different forms of pentadactyl limb in different vertebrate species as adaptations to different ways of living and moving.
What happens when organisms grow?
-When organisms grow they get bigger.
How do we observe growth?
-The easiest way to observe growth is to measure an increase in size, length or mass.
-For example, health professionals measure the mass and height of babies and children regularly to check that they are growing normally. Each child is compared to a chart to find out which percentile of the population hey fall into.
Why can measuring growth be difficult?
-You have to be careful when you measure growth. When you blow up a balloon it gets bigger but the amount of balloon material is the same.
What does growth in a living organism involve?
-Growth in a living organism involves two processes. There is an increase in the number of cells when a cell divides to form two identical calls, and then these get bigger.
How do plants grow?
-Plants grow all through their lives. Plant have special areas called 'meristems' just behind the tip of their roots and shoots where the cells keep dividing. However, growth in plants isn't just about cell division. Once the cells have divided they get longer (elongation)
-As a plant stem or root continues to grow, the older meristem cells start to become specialised - they differentiate.A meristem cell can differentiate into any type of plant cell. For example, a cell in a shoot can become a leaf cell containing chlorophyll or a new cell in a root can differentiate to become a root hair cell.
How do animals grow?
-Growth in animals involves cell division. But animals differ from plants because they stop growing when they become adults.
-In an animals, cells can differentiate to form a number of different types of specialised cells are called stem cells. These cells develop into specialised tissues and organs of an animal's body.
-In an embryo, the stem cells can differentiate and form almost every type of cell needed in the body.
-Adults have relatively few stem cells. Each type of adult stem cell can only form a limited range of cells, such as blood cells or skeletal tissue. This is why most animals cannot re-grow a damaged limb or body part but plants can grow new shoots,roots and leaves.
What is blood?
-Although blood is a liquid, it is also an organ containing many different types of specialised cells that carry out particular functions in our body. These have all differentiated from blood stem cells and become specialised.
-An adult has about 5 litres of blood.
What is blood made up of?
-Blood is made up of fur main components;
-Red blood cells (45%)
-White blood cells
-Platelets (<1% (with white blood cells))
What is plasma?
-Plasma is a yellow liquid. It transports dissolved substances, such as carbon dioxide, food substances and hormones.
What are red blood cells?
-Red blood cells contain the red pigment haemoglobin. Haemoglobin can combine reversibly with oxygen to form oxyhaemoglobin.
-haemoglobin + oxygen oxyhaemoglobin
-When oxygen passes through the lungs the haemoglobin combines with oxygen. Oxyhaemoglobin is transported in red blood cells around the body to the tissue, where the oxygen is then released so that the tissue cells have oxygen for aerobic respiration.
-A red blood cell has the shape of a biconcave disc - it has a dimple of both side. This adaptation gives a large surface area to volume ratio for oxygen to diffuse in and out of the cell. A red blood cell also has no nucleus and this makes room for as much haemoglobin as possible.
What are white blood cells?
-White blood cells are part of the body's defences against disease. Some white blood cells make antibodies. These are proteins that bind to the microorganisms that cause disease and destroy them. Other white blood cells surround and destroy any foreign cells that get into the body. All white blood cells have a nucleus.
What are platelets?
-Platelets are tiny fragments of cells (and so do not have nuclei). They are important in making blood clot if you cut or damage your blood vessels. The clot dries out and forms a scab which also stops microorganisms getting into the body.
How is tissue formed?
-A group of the same type of specialised cells forms a tissue (e.g. muscle tissue is made of muscle cells).
What is an organ?
-An organ contains several different tissues working together to carry out a particular function in the body.
What is the function of the heart?
-The heart is an organ that pumps blood to the lungs and around the body. The heart needs to push blood around the body as a force and to give the blood pressure.
-Blood coming from the tissues is low in oxygen (deoxygenated). It is pumped by the heart to the lungs where the haemoglobin in red blood cells picks up oxygen and the blood becomes oxygenated. This oxygenated blood returns to the heart and is pumped around the body to the tissues and cells.
Why are there two sides of the heart?
-The left and right sides of the heart work together, filling and emptying at the same time. The two sides of the heart are completely separated by the muscular septum. There are two separate sides to keeps the oxygenated blood and the deoxygenated blood separate.
How does the deoxygenated blood enter the heart?
-A vena cave brings blood into the right atrium. When the atrium is full, muscles in the wall contract and force the blood through the valves into the right ventricle.
How does the deoxygenated blood leave the heart?
-When the ventricle is full of blood, the muscles of the ventricle wall contract forcing blood out through more valves into the pulmonary artery. This carries deoxygenated blood to the lungs where it picks up oxygen.
How does the oxygenated blood enter the heart?
-The oxygenated blood returns from the lungs to the left atrium of the heart in the pulmonary vein. When the atrium is full, it contracts and forces the blood through valves into the left ventricle.
How does oxygenated blood leave the heart?
--Once the ventricle is full of oxygenated blood the muscles of the ventricle wall contract. This forces blood out through more valves into the aorta. The aorta is the large blood vessel that carries oxygenated blood around the body.
Why are there valves between the atria and the ventricles?
-The valves are flaps of tissue that stop the blood flowing backwards, and just in one direction instead.
Why does the left ventricle have a thicker muscular wall than the right ventricle?
-The muscle wall of the left ventricle is thicker that that of the right ventricle because it has to pump all around the body rather than just to the lungs.
What path does blood take around the body?
-vein-->right atrium-->valve-->right ventricle-->artery-->lungs-->left atrium-->right ventricle-->artery-->tissues and cells-->vein
What else does the blood need to pump round the body other than the heart?
-The heart pumps blood around the body so that all the cells in the body can get the oxygen and nutrients that they need. However, it is not the only organ that helps to do this. Blood vessels are also needed.
What are the three types of blood vessels?
-Blood vessels are tube-shaped organs that carry blood. There are three types; arteries, capillaries and veins.
What are arteries?
-Arteries carry blood away from the heart. The blood in arteries has to be under high pressure so that it can reach all parts of the body. So arteries have strong, thick walls, and touch connective tissue.
What are capillaries?
-Capillaries allow substances to diffuse into and out of the blood into, the cells in tissues. To help this process capillaries have very thin walls.
What are veins?
-Veins have wide passages inside them and carry blood to the heart. They are wide and have a thin muscle layer because the blood flows relatively slow under low pressure.
What are groups of organs called?
-Groups of organs that work together are called organ systems.
What does the heart and blood vessels form?
-The heart and blood vessels form an organ system called the circulatory system.
Why does food have to be broken down?
-Food contains a lot of large insoluble molecules than cannot get into the blood. These need to be broken down into small soluble molecules such as glucose, which can pass into the blood and so be used in cells.
How id food broken down?
-Food is broken down in a process called digestion, which takes place in an organ system called the digestive system.
What is the digestive system made up of?
-The digestive system is made up of the alimentary canal, a muscular tube running through the body from mouth to anus, and several other organs that make chemicals needed for digestion (including enzymes).
What are the parts of the digestive system?
What is the job of the mouth?
-The mouth is where food is taken into the body. During chewing, teeth break up food into small pieces. This increases the surface area for digestive enzymes to work on. The tongue helps to form the chewed food into a ball called bolus. The bolus gets coated in saliva, which lubricates it and makes it easier to swallow Saliva also contains an enzyme that starts to break down the starch in food.
What is the job of the oesophagus?
-The oesophagus is a muscular tube between the mouth and the stomach. Muscles contract in waves to squeeze food down towards the stomach. This is called peristalsis. Peristalsis takes place all through the digestive system, pushing the food along the alimentary canal.
What is the job of the stomach?
-The stomach is a muscular bag that makes acid and some enzymes (most importantly, enzymes to digest proteins). It churns the food up with these juices by peristalsis to make a thick paste.
What is the job of the small intestine?
-The small intestine in a long, coiled, muscular tube where most of the large insoluble food molecules are broken down into smaller soluble molecules. It contains lots of digestive enzymes made by the pancreas and it makes its own digestive enzymes as well. The molecules of digested food are absorbed into the blood using finger-shaped projections called villi, which contain capillaries. Food is moved along by peristalsis.
What is the job of the pancreas?
-Th pancreas makes digestive enzymes and releases them into the first part of the small intestine.
What is the job of the large intestine?
-Undigested food passes into the large intestine, a wide thin-walled tube. Water diffuses back into the blood leaving the waste material (faeces) behind.
What is the job of the anus?
-Where the undigested food is passed out of the body.
What is the job of the liver?
-Digested food is absorbed by the small intestine and dissolves in the blood plasma. Once in the blood, it is taken to the liver to be processed. Some of the molecules are broken down even more. Some are built up into larger molecules again. The liver also makes bile, which helps the digestion of fats.
What is the job of the gall bladder?
-The gall bladder is a small organ that stores the bile made by the liver and releases it into the small intestine where it is needed.
What does the chemical breakdown depend on?
-The chemical breakdown of food depends on digestive enzymes. Different digestive enzyme break down the three main types of food molecules;
How are carbohydrates digested?
-Foods like bread and potatoes are full of carbohydrates (substances made of carbon, hydrogen and oxygen).
-The simplest carbohydrates are called sugars and these can be built up into more complex carbohydrates such as starch.
-The digestive enzymes that break down carbohydrates are known as carbohydrases.
-Amylase is a carbohydrase that breaks down starch into sugars,which can then be absorbed by the small intestine or broken down into glucose by other carbohydrases.
-An amylase is present in saliva. Another amylase is made in the pancreas and released into the small intestine.
How are proteins digested?
-Proteases are the enzymes that digest proteins, breaking them down into shorter chains and then into amino acids.
-Pepsin is a protease made in the stomach and it works best in acidic conditions. The stomach walls produce an acid, which makes the pH 2-3. This is the optimum pH for pepsin to break down protein as fast as possible. However, the contents of the small intestine are alkaline and so the proteases released into the smll intestine work best at about pH 8.
How are fats digested?
-Lipases are the enzymes that digest fats. Lipases chemically break down fat molecules into fatty acids and glycerol.
What is the role of bile in digestion?
-Fat and water don't mix so the fats and oils you eat form globules in the watery digestive juices. Large globules have a very small surface area to volume ratio, which means the lipases can only break down the fat molecules very slowly.
-However, bile physically breaks down the large globules into tiny droplets, forming an emulsion. We say that bile emulsifies the fat. The smaller droplets have a larger surface area, which makes it possible for lipases to break down the fat molecules far more rapidly. More bile is released after a fatty meal. Bile makes faeces brown
-The bile from the gall bladder is alkaline. This helps to neutralise the acid from the stomach and produces a slightly alkaline environment for the protease enzymes of the small intestine to work in.
How does digested food enter the blood stream?
-Digested food passes into the blood by diffusion through the intestine and capillary walls. The bigger the surface available, the more diffusion can take place.
What is the role of villi in digestion?
-The small intestine is a tube about 5m long and 2.5cm in diameter. If the inside surface was smooth the surface area would only be about 0.5m2 and very little abbsorbtion would take place.
-However, the lining of the small intestine has millions of finger-like folds called villi that make the surface area much bigger. If it were opened out, the surface area would actually be about 200m2. This means much more diffusion can take place.
What is the structure of villi?
-Each villus has a good network of blood capillaries. This means there is always a lower concentration of soluble food molecules in the blood than there is inside the small intestine because soluble food molecules are constantly moved away in the blood. This steep concentration gradient between the two areas means diffusion takes place rapidly down it.
-There is only one single layer of cells between the contents of the small intestine and the blood vessels in the villi. This means there is only a short distance over which the soluble food molecules need to diffuse. The large surface area, good blood supply and short distances all make the diffusion of dissolved food molecules into the blood as efficient as possible.
What evidence is there to show the importance of villi?
-Evidence that the villi are important for increasing the efficiency with which the soluble products of digestion are absorbed into the blood can come from studying coeliac disease. In this disease villi may be lost. People affected cannot absorb the products of digestion properly. They often become very thin as a result.
What are functional foods?
-Many healthy people now eat functional foods as well as their normal food. The foods claim to make you healthier.
How much bacteria does the digestive system contain?
-The digestive system contains about 100,000,000,000,000 (10(13)) bacteria. That's more bacteria than you have cells in your body. Some of these bacteria can cause problems but most provide health benefits. They help break down food and protect against disease-causing microorganisms.
What are probiotics?
-Probiotics contain live bacteria, often called 'friendly' or 'beneficial' bacteria. These are usually Lactobacillus and Bifidobacteria, which produce lactic acid in the gut.
What do probiotic food manufacturers claim and why has it been proved wrong by scientists?
-The manufacturers of probiotic foods, such as yoghurt or yoghurt drinks, claim that it will make you healthier by improving your digestive system, helping your body protect itself against disease and reducing allergies.
-In 2010, scientists at the European Food Safety Agency looked at evidence for 180 health claims for probiotics. They rejected 10 and said there was not enough evidence to support the 170 other claims.
What are plant stanol esters?
-Plant stanol esters are oily substances found in plants. Scientists have discovered that these can stop the small intestine absorbing cholesterol, lowering the levels of cholesterol in the blood. High cholesterol levels are linked to a raised risk of heart disease.
-Plant stanols are now used in many foods such as yoghurt, drinks and spreads. There is clear evidence that they have an effect.