Enzymes Describe enzymes as biological catalysts Enzymes catalyse chemical reactions occurring inside and outside living cells, including: a DNA replication b protein synthesis c digestion Describe the factors affecting enzyme action, including: a temperature b substrate concentration c pH Enzymes are highly specific for their substrate The action of enzymes in terms of the ‘lock-and-key’ hypothesis Describe how enzymes can be denatured due to changes in the shape of the active site

A student carried out an investigation to study the effect of pH on the activity of catalase. In the presence of catalase, hydrogen peroxide breaks down to release oxygen gas. The student set up five test tubes, as shown in the diagram, and observed the amount of oxygen gas released. Explain the effect of pH on the enzyme catalse.

Markscheme more oxygen given off at pH 7 pH 7 is the optimum pH for this enzyme reaction is faster/enzyme more active in neutral solution very little oxygen given off at pH 5 and pH 9 enzyme / catalase less active no oxygen given off at pH 1 and pH 14 no enzyme activity enzyme denatured shape of active site is changed due to strong acid / low pH/strong alkali / high pH no longer binds to hydrogen peroxide / substrate

Digestion Describe the functions of the parts of the digestive system, including: a mouth b oesophagus c stomach d small and large intestines e pancreas f liver g gall bladder Explain the role of the muscular wall of the alimentary canal in peristalsis Explain the role of digestive enzymes, including: a carbohydrases, including amylase, which digest starch to simple sugars b proteases, including pepsin, which digest proteins to amino acids c lipase, which digests fats to fatty acids and glycerol Explain the role of bile in neutralising stomach acid and emulsifying fats Explain how the structure of villi (large surface area, single layer of cells and capillary network) allows efficient absorption of the soluble products of digestion

Describe how the action of the mouth, oesophagus and stomach contribute to the digestion of food.

Markscheme mouth teeth chew food/break food down into smaller pieces increasing its surface area (and) mixes food with saliva so it can be swallowed more easily enzyme action in mouth / amylase Digests starch to sugar/glucose tongue helps to roll food into a ball/bolus (so it can be swallowed more easily) oesophagus swallowing muscular contractions/peristalsis in oesophagus pushes/moves food towards the stomach stomach contraction of muscle tissue in the stomach mixes food with acid and digestive juices enzyme action in stomach / protease Digests protein to amino aciids hydrochloric acid contributes to the breakdown of food

The diagram shows how visking tubing can be used to model the small intestine. This model does not fully represent the structure and functions of the small intestine. Evaluate the strengths and weaknesses of this model.

Markscheme Strengths thin membrane permeable membrane presence of amylase presence of (large) starch molecules digestion into glucose glucose diffuses out concentration gradient water represents the blood weaknesses membrane not one cell thick not a large surface area shorter length / not same size no villi /micro villi only carbohydrate digestion no other enzymes present no peristalsis no blood movement other factors e.g. pH

Describe the roles of the enzymes involved in digestion.

Markscheme Names of enzymes: carbohydrases eg amylase proteases eg pepsin lipases General points about enzyme action: breakdown of large / insoluble / named molecules into small soluble molecules for absorption catalysts speeds up reactions active sites that bind to substrate idea of specificity – each enzyme can only break down 1 food type Due to shape of active site only matching 1 food type Specific points: carbohydrates/ starch are broken down into sugars / glucose proteins /named protein are broken down into amino acids fats / oils / lipids / named lipid are broken down into fatty acids /glycerol

Describe the role of the small intestine in digestion

Markscheme Digestion Makes enzymes Receives enzymes from pancreas Enzyme amylase Breaks down starch into sugar Enzyme protease Breaks down protein into amino acids Enzyme lipase Breaks down fats into fatty acids and glycerol Receives bile from gall bladder Bile emulsifies fats Increasing SA Enzymes breaks fat down faster Absorption By diffusion Into blood stream Villi Increase SA so faster diffusion single layer of cells Short distance for substances to travel before getting into blood Good capillary network Maintains concentration gradient so diffusion happens quickly

Explain how the structure of the small intestine allows efficient absorption of the soluble products of digestion

Markscheme Long Villi Increase SA For diffusion single layer of cells Short distance for substances to travel before getting into blood Good capillary network Blood carries digested food around body Maintains concentration gradient So diffusion happens quickly

Transport in Plants Explain how the loss of water vapour from leaves drives transpiration Explain how water, glucose and mineral salts are transported through a plant, including: a mineral uptake in roots by active transport b the role of the xylem and phloem vessels Describe how root hair cells are adapted to take up water by osmosis Define osmosis as the movement of water molecules from an area of higher concentration of water to an area of lower concentration of water through a partially permeable membrane

Explain how water, glucose and mineral salts are transported through a plant.

Markscheme water through the xylem capillary action osmosis into cells in the leaf evaporation from leaves transpiration stream diffusion into the atmosphere through stomata glucose converted to sucrose dissolved in water through the phloem bidirectional mineral salts dissolved in water through the xylem from root to tip

Describe how water enters plants from the soil and is transported to the leaves.

Markscheme (water moves into) root hair cells by osmosis from a high concentration (of water) to a low concentration (of water) down a concentration gradient through a partially permeable membrane through xylem vessels by capillary action (into leaves) and out through the stomata reference to transpiration/transpiration stream

Photosynthesis Describe how the structure of a leaf is adapted for photosynthesis, including: a large surface area b containing chlorophyll in chloroplasts to absorb light c stomata for gas exchange (carbon dioxide, oxygen and water vapour) How photosynthesis uses light energy to produce glucose and how this process can be modelled using the word equation for photosynthesis How limiting factors affect the rate of photosynthesis, including: a light intensity b CO2 concentration c temperature

Describe how the structure of leaves is adapted for photosynthesis

Markscheme leaves have a large surface area contain (many) chloroplasts/chlorophyll for maximum absorption of light waxy cuticle to reduce water loss stomata/pores gas exchange/to take in carbon dioxide and release oxygen guard cells that control size of stoma xylem vessels throughout the leaf deliver water and mineral ions

Revision DNA and Protein Synthesis

In pairs………………. What is a gene? Describe the structure of DNA Name the scientists to discovered the structure of DNA What did they do?

DNA Recall that a gene is a section of DNA and that it codes for a specific protein Describe a DNA molecule as: – a two strands coiled to form a double helix – b strands linked by a series of complementary base pairs joined together by weak hydrogen bonds: i adenine (A) with thymine (T) ii cytosine (C) with guanine (G) Explain how the structure of DNA was discovered, including the roles of the scientists Watson, Crick, Franklin and Wilkins Investigate how to extract DNA from cells

Describe the structure of DNA, including the roles of the scientists involved in its discovery.

Markscheme DNA structure (max 3) two strands twisted into a double helix (contains) bases A, T, C, G adenine / A paired with thymine / T guanine / G paired with cytosine / C hydrogen / H bonds joining bases Contributions from Scientists (max 3) Franklin & Wilkins - X-ray (crystallography) being used – to show helical structure – to show diameter of molecule – how base pairs are arranged was shown – how strands are arranged was shown Watson &Crick - Building models – Used Franklin and Watsons X rays to work out shape

DNA Recall that a gene is a section of DNA and that it codes for a specific protein Describe a DNA molecule as: – a two strands coiled to form a double helix – b strands linked by a series of complementary base pairs joined together by weak hydrogen bonds: i adenine (A) with thymine (T) ii cytosine (C) with guanine (G) Explain how the structure of DNA was discovered, including the roles of the scientists Watson, Crick, Franklin and Wilkins Investigate how to extract DNA from cells

Protein Synthesis Demonstrate an understanding of the stages of protein synthesis - transcription and translation: – a the production of complementary mRNA strand in the – nucleus – b the attachment of the mRNA to the ribosome – c the coding by triplets of bases (codons) in the mRNA – for specific amino acids – d the transfer of amino acids to the ribosome by tRNA – e the linking of amino acids to form polypeptides Describe each protein as having a specific number and sequence of amino acids, resulting in different-shaped proteins that have different functions, including enzymes Demonstrate an understanding of how gene mutations change the DNA base sequence and mutations can be harmful, beneficial or neither

Describe how the order of bases in a section of DNA decides the order of amino acids in the protein

Markscheme Transcription mRNA made In nucleus Complimentary copy of gene By complimentary base pairing Translation: mRNA attaches to the ribosome Each 3 bases (codons) in the mRNA codes for specific amino acids transfer of amino acids to the ribosome by tRNA the linking of amino acids to form polypeptides

Describe the effect of a mutation

Markscheme Change in a gene Change to sequence/order of bases Changes order or type of amino acid Changes shape of protein Function of protein changes Enzymes active site changes shape Substrate can’t fit into it May have useful effect eg new characteristic May have harmful effect – eg cancer May have no effect on characteristic

Gene Technology The process of genetic engineering, including the removal of a gene from the DNA of one organism and the insertion of that gene into the DNA of another organism Advantages and disadvantages of genetic engineering to produce GM organisms, – a beta carotene in golden rice to reduce vitamin A deficiency in humans – b the production of human insulin by genetically modified bacteria – c the production of herbicide-resistant crop plants Recall that cloning is an example of asexual reproduction that produces genetically identical copies The stages in the production of cloned mammals, including: – a removal of diploid nucleus from a body cell – b enucleation of egg cell – c insertion of diploid nucleus into enucleated egg cell – d stimulation of the diploid nucleus to divide by mitosis – e implantation into surrogate mammals The advantages, disadvantages and risks of cloning mammals Stem cells in the embryo can differentiate into all other types of cells, but that cells lose this ability as the animal matures The advantages, disadvantages and risks arising from adult and embryonic stem cell research

Genetic engineering can be used to produce GM organisms. Describe process of genetic engineering

Markscheme removal of a gene from the DNA of one organism Cut out using an enzymes gene inserted into the DNA of other organism using enzymes Gene codes for new protein

Evaluate the use of genetic engineering to produce GM organisms

Markscheme Advantages beta carotene in golden rice to reduce vitamin A deficiency in humans Of bacteria to produce human insulin To treat diabetes Production of herbicide-resistant crop plants Easier for farmers to spray fields to get rid of weeds Disadvantages Unexpected effects Makes crops poisonous Bacteria – new diseases herbicide-resistant gene gets into wild plants

Evaluate the use of adult and embryonic stem cells in research.

Markscheme Advantages Stem cells can differentiate into any cell type Can lead to treatments for disease Eg fix damaged heart muscle Disadvantages Embryonic stem cells – have to kill embryo. Some people think this is wrong as it is an unborn baby Adult stem cells – not many in an adult, hard to get Adult stem cell treatment don’t always work body destroys them Stem cells injected into body could cause cancer

A cloned animal contains genetic information that is identical to its parent. Describe the stages in the production of a cloned mammal.

Markscheme use of body cell nucleus removed from body / parent cell use of egg cell - nucleus removed from egg cell nucleus (from body cell) transferred to empty egg electric shock; to stimulate cell division Mitosis happens formation of embryo; embryo implanted into womb of female – pregnancy happens normally

Describe the processes that take place in the formation of the foetus from a sperm cell and an egg cell.

Markscheme fertilisation of egg by sperm fusion of nuclei forming diploid cell Forms zygote (zygote) divides by mitosis to form identical cells several mitotic divisions - growth of foetus examples of how fetus grows eg in height, mass stem cells in embryo specialisation / differentiation of (stem) cells into different cell types examples of different cell types eg neurones, skin cells

Cell Division Describe the division of a cell by mitosis as – the production of two daughter cells – each with identical sets of chromosomes in the nucleus to the parent cell – this results in the formation of two genetically identical diploid body cells Mitosis occurs during growth, repair and asexual reproduction At fertilisation, haploid gametes combine to form a diploid zygote Describe the division of a cell by meiosis as the production of – four daughter cells, – each with half the number of chromosomes – results in the formation of genetically different haploid gametes

Mitosis and meiosis are types of cell division. Compare these two types of cell division.

Markscheme Mitosis (genetically) identical cells produced two daughter cells one division diploid daughter cells occurs in the formation of body cells for growth and repair (of body tissues) Meiosis (genetically) non-identical cells four daughter cells 2 divisions haploid daughter cells half the number of chromosomes occurs in the formation of gametes results in genetic variation

Sperm cells and egg cells are needed for human sexual reproduction. Describe in detail the type of cell division that produces sperm cells.

Markscheme meiosis 2 divisions 4 cells produced haploid (cells) cells have half the number of chromosomes cells are genetically different (genetically) non- identical cells

Heart and Circulation How the structure of the heart is related to its function, : a four blood vessels of the heart (pulmonary artery, pulmonary vein, aorta, vena cava) b left atrium and ventricle to pump oxygenated blood c right atrium and ventricle to pump deoxygenated blood d valves to prevent backflow e why the left ventricle has a thicker muscle wall than the right ventricle f the direction of blood flow through the heart Structure and function of arteries, veins, capillaries. a arteries transport blood away from the heart b veins transport blood to the heart c capillaries exchange materials with tissues Structure and function of the parts of the blood, : a red blood cells b white blood cells c plasma d platelets glucose and oxygen diffuses from capillaries into respiring cells, carbon dioxide diffuses from respiring cells into capillaries Define diffusion as the movement of particles from an area of high concentration to an area of lower concentration

Markscheme two sides to prevent mixing of blood left side deals with oxygenated blood thicker wall of left ventricles pump blood to body right side deals with deoxygenated blood pumps blood to lungs muscular wall of ventricles which contract atria receive blood valves to prevent backflow correct reference to (named) arteries/veins

Explain why heart rate and breathing rate increase during exercise.

Markscheme increased muscle contraction blood is pumped faster around the body/to muscles more oxygen/glucose delivered to cells/muscles for aerobic respiration which releases energy rate of gas exchange increases more carbon dioxide in the blood more oxygen inhaled/into body more carbon dioxide exhaled/from body reduce build up of lactic acid

Exercise Investigate the effect of exercise on breathing rate and heart rate Explain why heart rate and breathing rate increase with exercise Calculate heart rate, stroke volume and cardiac output, using the equation, cardiac output = stroke volume x heart rate Why during vigorous exercise, muscle cells may not receive sufficient oxygen for their energy requirements and start to respire anaerobically

A reduced cardiac output would affect the performance of an athlete. Explain the effects that a reduced cardiac output would have on the muscle cells of an athlete.

Markscheme there will less blood flow (to the muscles) because less blood leaving the heart less oxygen (reaching muscle) less glucose (reaching muscle) reduced rate of aerobic respiration less energy released less carbon dioxide removed greater rate of anaerobic respiration glucose broken down without oxygen reduced muscle contraction build up of lactic acid (in muscle cells) causing cramp / fatigue

Respiration Aerobic respiration uses oxygen to release energy from glucose Word equation for aerobic respiration During vigorous exercise, muscle cells may not receive sufficient oxygen for their energy requirements and so start to respire anaerobically Anaerobic respiration releases energy from glucose Word equation for anaerobic respiration The process of anaerobic respiration releases less energy than aerobic respiration The build-up of lactic acid requires extra oxygen to break it down. This is called excess post-exercise oxygen consumption or EPOC (formerly known as oxygen debt) Explain why heart rate and breathing rate remain high after exercise

Compare aerobic and anaerobic respiration

Markscheme Aerobic Use oxygen To release energy from glucose Makes carbon dioxide and water Happens in all cells Anaerobic Does not use oxygen Releases less energy from glucose Makes lactic acid Happens in muscle cells During vigorous exercise When there is not enough oxygen

Explain why heart rate and breathing rate remain high after exercise

Markscheme rate of gas exchange increases in lungs more oxygen into body blood is pumped faster to muscles Red blood cells carry oxygen more oxygen gets to muscles Used to break down lactic acid made by anaerobic respiration called excess post-exercise oxygen consumption or EPOC