Biology revision a level exams

What is genetic diversity?
The number of different alleles of genes in a population
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What is a community?
All the populations of different species in a habitat
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What is taxonomy?
The science of classification. It involves naming organisms and organising them into groups.
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What is the founder effect?
When just a few organisms from a population start a new colony and there are only a small number of different alleles in the initial gene pool.
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What is forced expiratory volume?
The maximum volume of air that can be breathed out in 1 second.
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What is forced vital capacity?
The maximum volume of air it is possible to breathe forcefully out of the lungs.
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Give ways in which insects reduce water loss?
They have a waterproof, waxy cuticle to reduce evaporation and tiny hairs around their spiracles to reduce evaporation.
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What is a polar molecule?
A molecule with a partial negative charge on one side and a partial positive charge on the other.
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What are the 4 functions of proteins?
Enzymes/ Antibodies/ Transport proteins/ Structural proteins
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Explain how pH affects enzyme catalysis?
A change in pH alters the charges on the amino acids that make up the active site. This means the substrate can no longer bind to the active site.
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Explain how substrate concentration affects enzyme catalysis?
The higher the substrate concentration, the faster the reaction- more substrate molecules means a collision between substrate + enzyme is more likely and so more active sites will be used.
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Explain how enzyme concentration affects enzyme catalysis?
The more enzyme molecules there are in a solution, the more likely a substrate molecule is to collide with one and form a E-S complex. If the amount of substrate is limited it will level off.
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Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA.
Weak / easily broken hydrogen bonds between bases allow two strands to separate / unzip; 2. Two strands, so both can act as templates
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Give two structural differences between a molecule of messenger RNA (mRNA) and a molecule of transfer RNA (tRNA).
1. mRNA does not have hydrogen bonds / base pairing, tRNA doemRNA does not have an amino acid binding site, tRNA doesmRNA has codons, tRNA has an anticodons.
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Describe Transcription? (6 marks)
1. Helicase 2. Breaks hydrogen bonds 3. Only one DNA strand acts as template 4. RNA nucleotides attracted to exposed bases 5. Attraction according to base pairing 6. RNA polymerase joins RNA nucleotides together 7. Pre-mRNA spliced
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Describe Translation? (5 marks)
1.mRNA associates with a ribosome 2. Ribosome moves to start codon 3. tRNA brings amino acids 4. Anticodon on tRNA is complementary to codon on mRNA. 5. Ribosome moves along to next codon. 6. Process repeated + amino acids join by peptide bonds
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State and explain the property of water that can help to buffer changes in temperature?
1. (water has a relatively) high (specific) heat capacity; 2. Can gain / lose a lot of heat / energy without changing temperature.
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Describe how a peptide bond is formed between two amino acids to form a dipeptide
1. Condensation (reaction) / loss of water; 2. Between amine / NH2 and carboxyl / COOH.
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Two proteins have the same number and type of amino acids but different tertiary structures. Explain why.
Different sequence of amino acids. Forms ionic / hydrogen / disulfide bonds in different places;
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Explain why oxygen uptake is a measure of metabolic rate in organisms. [
(Oxygen used in) respiration, which provides energy / ATP;
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The mass flow hypothesis is used to explain the movement of substances through phloem. Evaluate whether the information from this investigation supports this hypothesis
No bulge above ringing (in F); 7. No (role for) osmosis / hydrostatic pressure / water movement; 8. Movement could be due to gravity; 9. Roots still grow without (intact/functioning) phloem; 10. No leaves / sugars / photosynthesis to act as a source;
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Describe how he made a 1 in 10 dilution and then used this to make a 1 in 1000 dilution of the original liquid culture of bacteria?
Add 1 part (bacteria) culture to 9 parts (sterile) liquid (to make 101 dilution); 2. Mix (well); 3. Repeat using 9 parts fresh (sterile) liquid and 1 part of 101 and 102 dilutions to make 103 dilution
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Explain the role of the heart in the formation of tissue fluid.
Contraction of ventricle(s) produces high blood / hydrostatic pressure; 2. (This) forces water (and some dissolved substances) out (of blood capillaries
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Suggest how a blockage in the lymphatic system could cause lymphoedema.
Excess tissue fluid cannot be (re)absorbed / builds up;
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What is meant in the t-test if p is les than 0.05
The difference is significant/not due to chance becasue is less than 0.05
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Describe the process of crossing over and explain how it increases genetic diversity. [
Homologous pairs of chromosomes associate / form a bivalent; 2. Chiasma(ta) form; 3. (Equal) lengths of (non-sister) chromatids / alleles are exchanged; 4. Producing new combinations of alleles
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Water has a high latent heat of vaporisation, what does this mean?
A lot of energy is used up when water evaporates. This is useful for living organisms becasue it means they can use water loss through evaporation to cool down without losing too uch water.
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Water has a high specific heat capacity, what does this mean?
It takes a lot of energy to heat it up. This is useful for living organisms beacsue water doesnt experience rapid temperature changes. This makes water a good habitat becasue it is stable.
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How does waters polarity make it a good solvent?
Becasue water is polar, the positive end of a water molecule will be attracted to the negative ion, and the negative end will be attracted the positive ion. This means the ions will get totally surrounded by water molecules.
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Describe the cohesive properties of water?
Water molecules are very cohesive because they are polar. Strong cohesion means that water has a high surface tension when it comes into contact with air. This is why sweat forms droplets, which evaporate to cool an organism down.
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What is meant by universal?
The same specific base triplets code for the same amino acids in all living things.
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What is non-disjunction?
The failure of homologous chromosomes to separate during cell division.
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Describe how antibiotic resistance shows directional selection?
1. Some individuals in a population have alleles that give them resistance to an antibiotic. 2. That population is exposed to the antibiotic, killing bacteria without the resistant allele.
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Antibiotic resistance continued?
3.The resistant bacteria survive and reproduce without competition, passing on the allele that gives antibiotic resistance to their offspring. 4. After time, most organisms will carry the antibiotic resistance allele.
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Give three ways in which courtship behaviour increases the probability of successful mating?
Recognise same species/ Recognition of opposite sex/ Indication of sexual maturity
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What is a hierarchy?
Groups within groups, no overlap between groups.
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What is meant by gene pool?
The complete range of alleles present in a population
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What is a population?
A group of organisms of the same species living in a particular area at a particular time.
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What is the function of the coronary arteries?
To supply the heart muscle with blood.
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Explain what is meant by a double circulatory system
A double circulatory system refers to a system in which blood pumps through the heart twice during each trip around the body. The blood is first pumped into the lungs, where it becomes oxygenated, and is then pumped back into the heart.
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Explain the cooperative nature of oxygen binding, with the binding of the first oxygen molecule making the binding of subsequent oxygen molecules easier.
When haemoglobin combines with the first oxygen molecule, its shape alters in a way that makes it easier for other molecules to join too.
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What is pulmonary tuberculosis?
Forms tubercles. The gas exchange surface is damaged, so tidal volume is reduced menaing less air can be inhaled with each breathe. Vnetilation rate increases.
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What is fibrosis?
The formation of scar tissue in the lungs. This can be the result of an infection or exposure to dust. Scar tissue is thicker + less elastic. Lungs are less able to expand so tidal volume is reduced.
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What is asthma?
Where the airways become inflamed and irritated caused by allergic reaction to dust. Smooth muscle lining the bronchioles contracts + mucus is produced. Causes constriction of airways making it difficult to breathe.
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What is lung emphysema?
Caused by smoking or long-term exposure to air pollution. This causes inflammation, which attracts phagocytes. Breaks down elastin so alveoli cant recoil. It also leads to the destruction of the alveoli walls.
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When can a molecule pass through the cell membrane by diffusion?
A molecule can diffuse passively through the cell membrane if it’s lipid-soluble, uncharged, and very small,
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Describe the structure of arteries?
Their walls are thick and muscular and have elastic tissue to stretch and resoil as the heart beats, which helps maintain the high pressure. All arteries carry oxygenated blood except pulmonary artery.
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Describe the structure of veins?
Veins have a wider lumen with very little elastic or muscle tissue. Contain valves. All veins carry deoxygenated blood except the pulmnary vein which carry oxygenated blood.
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Describe the structure of arterioles?
Arterioles carry blood under lower pressure than arteries, from arteries to capillaries. The muscle layer is thicker than in arteries. The elastic layer is thinner than in arteries.
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Describe capillaries?
Tiny vessels that link arterioles to veins. Their walls consist mostly of the lining layer making them thin. They are numerous + highly branched. Their lumen is narrow.
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Describe the formation of tissue fluid?
Pumping by the heart creates hydrostatic pressure at the arterial end of the capillaries. This hydrostatic pressure casues tissue fluid to move out of blood plasma
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Describe tissue fluids return to the circulatory system?
1. The loss of the tissue fluid from the capillaries reduces the hydrostatic pressure. 2. By the time blood has reached the venous end its hydrostatic pressure is lower than the tissue fluid otside it.
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stages 3, 4,5?
3. Therefore tissue fluid is forced back into the capillaries by the higher hydrostatic pressure outside of them. 4. The plasma has lost water + still contains proteins. It has a lower water potential than the tissue fluid. 5. Water leaves the tissue
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What is meant by a hypertonic solution?
A hypertonic solution contains a higher concentration of solutes compared to another solution.
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What is a hypotonic solution?
a hypotonic solution has a lower concentration of solutes outside the cell than inside the cell.
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What are the functions of the golgi apparatus?
Add carbohydrates to proteins to form glycoproteins/ Forms lysosomes/ Transport, modify and store lipids/secrete carbohydrates
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When water potential is high ( less negative) what happens to the movement of water?
Water enters the cell and the cell swells and bursts. For a lower water potential (more negative water leaves the cell and the cell shrinks.
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How does co-transport work?
1. They bind 2 molecules at a time. 2. The concentration gradient of one molecule is used to move the other molecule against its own concentration gradient.
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How does glucose enter the ileum epithelium with sodium ions?
1. Sodium ions are actively transported out of the ileum epithelial cells, into the blood by the sodium-potassium pump. This creates a concentration gradient. 2. This causes sodium ions to diffuse from the lumen of the ileum into the epithelial cell
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Stage 3 + 4?
3. The co-transporter carries glucose into the cell with the sodium. As a result the concentration of glucose inside the cell increases. 4. Glucose diffuses out of the cell, into the blood, down its concentration gradient ghrough a protein channel.
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An antibody has 2 binding sites, what does this mean?
The antibody has 2 binding sites, so can bind to 2 pathogens at the same time. This means that pathogens become clumped together-agglutination.
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What does the specificity of antibodies depend on?
The specificity of an antibody depends on its variable regions, which form the antigen binding sites. Each antibody has a variable region with a unique tertiary structure thats complementary to 1 specific antigen.
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Why dont antibiotics work against viruses?
Viruses dont have their own enzymes and ribosomes- they use the ones in the host cells. So becasue human viruses use human enzymes and ribosomes to replicate, antibotics cant inhibit them because they dont target human processes.
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Describe the induced-fit model of enzyme action?
The active site is not complementary to the substrate so the active site changes shape. This stresses/distorts bonds.
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Water and oxygen flows over the gill in the opposite direction to the blood flow inside. Explain why this arrangement is important for efficient oxygen uptake?
Maintains diffusion gradient, diffusion occurs across whole length of gill .
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What is the difference between channel proteins and carrier proteins?
Channel proteins allow charged ions to pass through. Carrier proteins allow large polar molecule to pass through.
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What is evidence for Mass Flow?
1. Bulge forming- th fluid from the bulge has a higher concentration of sugars than the fluid from below the ring. Evidence there is a downward flow of sugars. 2. If a metabolic inhibitor is put into the phloem, then translocation stops- Evidence AT.
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Objections of Mass Flow?
1. Sugar travels to many different sinks, not just the one with the highest water potential. 2. The sieve plates would create a barrier to mass flow. A lot of pressure would be needed for the solutes to get through.
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Give 5 types of agricultural practices to reduce biodiversity?
Woodland clearance/ Hedgerow removal/ Pesticides/ Herbicides/ Monoculture
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In a potometer why cut a shoot underwater, why cut it at a slant?
1. To prevent air from entering the xylem 2. To increase the SA available for water uptake.
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Card 2


What is a community?


All the populations of different species in a habitat

Card 3


What is taxonomy?


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Card 4


What is the founder effect?


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Card 5


What is forced expiratory volume?


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