CO2 Concentration, Light intensity and temperature are limiting factors of photosynthesis.
For light intensity, it is proportional to the rate of photosynthesis up to a point. During this time, light intensity is the limiting factor. After this point, even if light intensity increases further, rate of photosynthesis will not be affected as something else is the limiting factor. The same is true for CO2 concentration.
For temperature, an increase in temperature will result in an increase in the rate of photosynthesis up to a point (25-30oC). After this point, the rate of photosynthesis will drop rapidly as enzymes required for the chemical reactions will become denatured.
2.20 Explain how the structure of the leaf is adapted for photosynthesis
- Leaf is green - contains chlorophyll
- Leaf has large surface area to absorb a lot of light
- The upper epidermis is transparent to allow light to reach photosynthesising cells within the leaf
- The palisade cells are tightly packed together to receive a lot of sunlight and contain most chloroplasts
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Spongy mesophyll layer has gaps to allow CO2 and O2 to move to and from cells
2.21 Recall that plants require mineral ions for growth and that magnesium ions are needed for chlorophyll and nitrate ions are needed for amino acids
A plant uses active transport to absorb mineral ions from the soil using roots.
Magnesium Ions - Chlorophyll - deficiency= yellow leaves
Nitrate Ions - Amino acids - deficiency= stunted growth
2.22 describe simple controlled experiments to investigate photosynthesis, showing the evolution of oxygen from a water plant, the production of starch and the requirements of light, carbon dioxide and chlorophyll
Oxygen - Put an underwater plant under a test tube and collect the gas that it evolves. Use a glowing splint test to figure out that this is oxygen.
Starch - Take a destarched plant and leave it in the light for an hour. Take a leaf from this plant and boil it in ethanol to remove chlorophyll and then use the iodine test
Light - Cover a part of a leaf on a destarched plant and use iodine test to see that only the part of the leave with access to light produced starch
CO2 - Get two bell jars, put a burning candle in one (to produce CO2), potassium hydroxide in the other (to remove CO2). Put similar destarched plants in the bell jars and attach the lid with petroleum jelly. Do iodine test after an hour and see how the no CO2 plant did not produce any starch
Chlorophyll - Use a variegated leaf for an iodine test, starch will only come up on the parts with chlorophyll
2.23 Understand that a balanced diet should include appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre
Proportion is important as some foods contain more than one kind of nutrient and we need more of some nutrients than others
2.24 Recall sources and describe functions of carbohydrate, protein, lipid (fats and oils), vitamins A, C and D, and the mineral ions calcium and iron, water and dietary fibre as components of the diet
Carbohydrates: Rice, Bread potatoes - Release energy in our cells so that life processes can take place
Protein: Eggs, Milk, Meat - Form enzymes and help us to grow
Lipids: Butter, Cheese, Nuts - Insulation to maintain body temperature; long term energy supply
Vitamin A: Liver, Carrots - Keeps skin healthy, helps eyes to see in poor light
Vitamin C: Citrus Fruits, - Keeps skin healthy, Keeps teeth and gums healthy, Maintains lining of blood vessels
Vitamin D: Fish, Eggs, Milk - Keeps bones and teeth strong
Calcium: Milk, Eggs - Keeps bones and teeth strong
Iron: Spinach, Kidneys - Needed to make haemoglobin in red blood cells to transport oxygen.
Water: Constantly being lost through excretion/sweat, major constituent of our body
Fibre: Cabbage, Wheat - Prevents constipation, gives the digestive system something to push on
2.25 Understand that energy requirements vary with activity levels, age and pregnancy
Children need more protein for growth. More iron needed during pregnancy to make blood cells for the baby. If we use more energy in a day, we need to consume the same amount.
2.26 Recognise the structures of the human alimentary canal and describe in outline the functions of the mouth, oesophagus, stomach, small intestine, large intestine and pancreas
2.29 Understand the role of digestive enzymes to include the digestion of starch to glucose by amylase and maltase, the digestion of proteins to amino acids by proteases and the digestion of lipids to fatty acids and glycerol by lipases
Mouth - Teeth and tongue mechanically break down food into smaller pieces. Salivary amylase is secreted by the salivary glands, which chemically breaks down starch to maltose
Oesophagus - Where peristalsis occurs - waves of longitudinal and circular muscle contraction push boluses of food to the stomach.
Stomach - Food is churned into chime. Hydrochloric acid kills microbes and provides an optimum pH for the enzyme pepsin (secreted by stomach walls) which digests proteins into peptides
Pancreas - Synthesises pancreatic juices; includes trypsin, which converts proteins to peptides and amylase, digesting starch into maltose.
Small intestine (Duodenum) - Chyme is mixed with pancreatic juices and bile. The wall of the small intestine then secretes maltase, digesting maltose to glucose and peptidase, digesting peptides to amino acids, as well as lipase which digests lipids into fatty acids and glycerol.
Small intestine (Ileum) - Villi and microvilli (large surface area) absorb the chyme. Fats go into the lacteal. Bile is absorbed here and returns to the liver.
2.27 Understand the processes of ingestion, digestion, absorption, assimilation and egestion
Ingestion - When food is taken in to the mouth
Digestion - The breakdown of food
Absorption - The crossing of the gut by small soluble food molecules into the bloodstream
Assimilation - Food is used by cells for energy, growth and repair
Egestion - Dietary fibre and other indigestible substances pass down the anus
2.28 Explain how and why food is moved through the gut by peristalsis
Circular muscles and longitudinal muscles contract and relax, making the lumen smaller and bigger consecutively, squeezing the bolus of food towards the stomach. Peristalsis is important to move food along the alimentary canal
2.30 Recall that bile is produced by the liver and stored in the gall bladder, and understand the role of bile in neutralising stomach acid and emulsifying lipids
Bile is highly alklaline so neutralises the chyme in the duodenum after it has been subject to the acidic gastric juices in the stomach. Bile emulsifies fat by lowering their surface tension so that they break up - mechanical digestion, large droplets → smaller ones.
2.31 Explain how the structure of a villus helps absorption of the products of digestion in the small intestine
Villi have low surface area to volume ratios
Microvilli further increases the surface area
Contain lacteals which carry fat droplets separately
Have a constant supply of blood, establishes a concentration gradient
2.32 Recall how to carry out a simple experiment to determine the energy content in a food sample.
Set it alight and see how well and how long it burns for.
2.33 Recall that the process of respiration releases energy in living organisms
2.34 Describe the differences between aerobic and anaerobic respiration
Aerobic respiration requires oxygen, whereas anaerobic does not
Aerobic respiration produces a significantly higher amount of energy than anaerobic
Anaerobic respiration produces lactic acid, whereas aerobic respiration does not
2.35 Recall the word equation and the balanced chemical symbol equation for aerobic respiration in living organisms
Glucose + Oxygen --------------> Carbon Dioxide + Water (+ Energy)
C6H12O6 + 6O2 --------------> 6CO2 + 6H2O (+ Energy)
2.36 Recall the word equation for anaerobic respiration in plants and in animals
ANIMALS Glucose ------------> Lactic Acid (+ Energy)
PLANTS Glucose ------------> Ethanol + Carbon Dioxide (+ Energy)
2.37 Describe simple controlled experiments to demonstrate the evolution of carbon dioxide and heat from respiring seeds or other suitable living organisms.
Lime Water in B is clear because sodalime in A absorbs CO2 in the air. This shows that the germinating seeds in C are producing CO2 as D is cloudy.
2.38 Understand the role of diffusion in gas exchange
In humans, gases diffuse across the alveoli into the blood. In plants, gases diffuse through the stomata
2.39 Understand gas exchange (of carbon dioxide and oxygen) in relation to respiration and photosynthesis
2.40 understand that respiration continues during the day and night, but that the net exchange of carbon dioxide and oxygen depends on the intensity of light
Photosynthesis occurs mainly during the daytime because of the light intensity but plants respire even during the night.
Compensation Point - The point at which respiration and photosynthesis produce and use equal amounts of carbon dioxide and oxygen
During daylight, oxygen production from photosynthesis exceeds its use in respiration and the opposite for carbon dioxide
2.41 explain how the structure of the leaf is adapted for gas exchange
- Large surface area
- Short distances between photosynthesising cells to the air spaces in the leaf
- Presence of stomata
2.42 describe the role of stomata in gas exchange
CO2 and oxygen enter and leave the plant through the stomata. When the leaf is exposed to light, the stomata open wider because this is when demand is greatest for gas exchange. The opening and closing of the stomata is controlled by the swelling of the guard cells.
2.43 Describe simple controlled experiments to investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator
Use a core borer to cut leaf disks and put these in petri dishes containing equilibrated hydrogencarbonate indicator. Placing one dish in bright light and covering the other dish in dark paper. After 10-15 minutes, the indicator in the covered dish would turn from red to yellow, showing an increase in carbon dioxide because photosynthesis has not occurred. The indicator in the bright light petri dish would turn from red to purple as there would be less carbon dioxide since it is being used up by photosynthesis at a faster rate than it is being produced by respiration
2.44 describe the structure of the thorax, including the ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli and pleural membranes
Air enters through the nose and mouth, travelling down the trachea. The trachea then sub divides into bronchi, which further subdivide into bronchioles, which lead to tiny air sacs where gas exchange takes place calls alveoli. Pleural membranes surround the lungs, an inner one attached to the lung surface, an outer one attached to the thoracic wall. Ribs protect the organs underneath, namely the heart and lungs; the ribs are joined together by intercostals muscles. The diaphragm is a large sheet that attaches to the thorax and sits underneath the lungs
2.45 understand the role of the intercostal muscles and the diaphragm in ventilation
Inhalation - Diaphragm contracts and flattens in shape. External intercostals muscles contract, making the ribs move upwards and outwards These cause the volume of the thorax to increase, causing pressure to decrease, drawing air into the lungs
Expiration - Diaphragm relaxes and returns to its dome shape. External intercostals muscles relax, allowing the ribs to move down and in. These cause the volume of the thorax to decrease and the pressure to increase, forcing air out of the lungs.
2.46 Explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries
- Walls are one cell thick, distance over which diffusion takes place is minimum
- Moist lining, so the gases dissolve before they cross
- A large surface area
- High concentration gradient for gases, due to good blood supply
2.47 Understand the biological consequences of smoking in relation to the lungs and the circulatory system
It could cause bronchitis because the tar sticks to the cilia in the windpipe and bronchi. It could cause emphysema, reducing the surface area of alveoli. It could cause cancer. Smoking causes cells to divide
2.48 Describe a simple experiment to investigate the effect of exercise on breathing in humans.
First choose a sample of people and measure their breathing rates at rest. Then make them vigorously exercise for two minutes and measure their breathing rates again
2.49 Understand why simple, unicellular organisms can rely on diffusion for movement of substances in and out of the cell
Unicellular organisms have a large enough surface area to volume ratio that diffusion occurs quickly enough to supply for the organism’s needs
2.50 Understand the need for a transport system in multicellular organisms
Diffusion becomes too slow to support the cells further away from the surface.
2.51 Describe the role of phloem in transporting sucrose and amino acids between the leaves and other parts of the plant
Phloem cells are living cells that are linked to form tissue. Phloem transports sugars and amino acids
2.52 Describe the role of the xylem in transporting water and mineral salts from the roots to other parts of the plant
Xylem cells transport water and minerals up the stem of the plant from roots to shoots. This transportation only occurs in one direction.
2.53 Explain how water is absorbed by root hair cells
Root hair cells have a large surface area - extension + hairs. Water enters the root hair cells via osmosis. This increases water potential in root hair cells, compared to the cells nearby, so water moves to these cells via osmosis etc... osmosis occurs through the xylem.
2.54 recall that transpiration is the evaporation of water from the surface of a plant
2.55 explain how the rate of transpiration is affected by changes in humidity, wind speed, temperature and light intensity
Humidity - When the air is humid underneath the stomata, the water potential is high, similar to the water potential inside the leaf so the concentration gradient will be very shallow and the rate of transpiration will be slow.
Wind speed - When there is a lot of wind, the air underneath the stomata will be constantly replaced, so when transpiration occurs, this air will be blown away, maintaining a steep concentration gradient, so rate of transpiration increases.
Temperature - A higher temperature means more kinetic energy for the particles. The faster the particles move, the easier it is for them to evaporate, so rate of transpiration increases.
Light Intensity - A high light intensity means that more photosynthesis is taking place, so the stomata will be open wider (because of gas exchange requirements). This makes it possible for water molecules to diffuse out of the air spaces into the air more quickly, increasing rate of transpiration
2.56 describe experiments that investigate the role of environmental factors in determining the rate of transpiration from a leafy shoot
Put a potometer in different sets of conditions (dark, light, windy, hot etc...) And note the time it takes for the bubble of water to move up the capillary tubing by 5cm. (It will only move up to replace the water lost through guard cells). Be sure to use rubber tubing and petroleum jelly to connect a plant and a photometer to ensure there are no air leaks.
2.57 Recall the composition of the blood: red blood cells, white blood cells, platelets and plasma
2.58 Understand the role of plasma in the transport of carbon dioxide, digested food, urea, hormones and heat energy
Plasma mainly consists of water, making it a good solvent so it digested food dissolves easily into plasma. Urea is also dissolved/transported via plasma. Hormones are also soluble in plasma.
2.59 Describe the adaptations of red blood cells for the transport of oxygen, including shape, structure and the presence of haemoglobin
- Biconcave disc shape - large surface area to volume ratio = faster diffusion and more oxygen
- Haemoglobin - carries oxygen
- No nucleus - more space to carry oxygen
- Small and flexible - can get through capillaries
2.60 Describe how the immune system responds to disease using white blood cells, illustrated by phagocytes ingesting pathogens and lymphocytes releasing antibodies specific to the pathogen
Phagocytes are involved in phagocytosis which engulfs and destroys pathogens. Pseudopodia surround the bacterium before the bacterium is enclosed in a vacuole where enzymes destroy it. Lymphocytes produce antibodies which specifically match a pathogen, attracting phagocytes or simply causing the pathogen to break open and die. Lymphocytes also produce memory cells which remain in the blood after the pathogen is destroyed
2.61 Understand that vaccination results in the manufacture of memory cells, which enable future antibody production to the pathogen to occur sooner, faster and in greater quantity
Vaccines give the body the impression of a pathogen so lymphocytes produce antibodies and more importantly memory cells. If you are ever exposed to the same pathogen, the memory cells act extremely fast to stimulate lymphocytes to release antibodies in greater quantities.
2.62 Recall that platelets are involved in blood clotting, which prevents blood loss and the entry of microorganisms
When there is damage to a blood vessel, platelets respond by releasing a chemical that causes the soluble fibre fibrinogen to turn to the insoluble fibrin, which acts as a clot. This prevents blood from getting out and microbes from getting in.
2.63 Describe the structure of the heart and how it functions
The heart consists of four chambers: two atria and two ventricles. Blood from the body arrives at the vena cava and enters the right atrium. Contraction of the right atrium passes blood on to the right ventricle. Contraction of this ventricle forces blood out through the pulmonary artery. Contraction of the left atrium passes blood to the left ventricle. Contraction of the left ventricle forces blood through the aorta. Valves ensure that blood only flows in one direction
When a chamber of the heart is contracting, we say it is in systole; when a chamber is relaxing, we say it is in diastole
2.64 Understand that the heart rate changes during exercise and under the influence of adrenaline
More energy is needed during exercise. Therefore more respiration is required in working muscles. Therefore more oxygen and glucose need to be supplied to muscles quicker. Therefore, heart pumps faster. Adrenaline causes the fight or flight response and prepares you for use of energy by increasing heart rate
2.65 Describe the structure of arteries, veins and capillaries and understand their roles
Arteries carry blood away from the heart. They carry blood at high pressure so need thick walls and a narrow lumen.
Veins vary blood back towards the heart so is at a lower pressure. There is usually no pulse. Veins have a large lumen o allow blood to flow easily back to the heart. Veins have valves to prevent backflow against the force of gravity.
Capillaries are very small and connect arteries to veins. Their wall is 1 cell thick. Exchange of substances including gaseous exchange occurs with capillaries.
2.66 Recall the general plan of the circulation system to include the blood vessels to and from the heart, the lungs, the liver and the kidneys.
2.67 Recall the origin of carbon dioxide and oxygen as waste products of metabolism and their loss from the stomata of a leaf
Carbon dioxide is produced in respiration while oxygen is a product of photosynthesis. Excess amounts of these gases are excreted through the stomata of leaves.
2.68 Recall that the lungs, kidneys and skin are organs of excretion
Lungs - carbon dioxide
Kidney - Urea + Other waste products
Skin - sweat (water + minerals)
2.69 Understand how the kidney carries out its roles of excretion and of osmoregulation
The kidney filters blood to remove waste substances no longer needed by the body
2.70 Describe the structure of the urinary system, including the kidneys, ureters, bladder and urethra
Two kidneys are situated just inside the ribcage at the back of the body about halfway down the spine. Kidneys filter the blood, removing waste to form urine. Urine flows out of the kidneys through the ureter and into the bladder. The urine is stored here until a ring of sphincter muscle relaxes; the urine then enters the environment via the urethra.
2.71 Describe the structure of a nephron, to include Bowman’s capsule and glomerulus, convoluted tubules, loop of Henlé and collecting duct
At the start of a nephron is a small cup-shaped structure called a Bowman’s capsule-This surrounds a knot of tiny capillaries called a glomerulus. The Bowman’s capsule leads into the proximal convoluted tubule. This leads into a long loop known as the loop of Henle. The loop leads into a second coiled tubule known as the distal convoluted tubule. This leads into the collecting duct.
2.72 Describe ultrafiltration in the Bowman’s capsule and the composition of the glomerular filtrate
Ultrafiltration is filtration on a molecular level. The walls of the Bowman’s capsule and capillaries are only one cell think, so the pressure of the blood in the glomerulus squeezes many small molecules out from the blood and into the capsule. These molecules include water, glucose, mineral ions, hormones, vitamins and urea, which together form the glomerular filtrate
2.73 Understand that water is reabsorbed into the blood from the collecting duct
The amount of water depends on the hydration state of the body
2.74 Understand that selective reabsorption of glucose occurs at the proximal convoluted tubule
2.75 Describe the role of ADH in regulating the water content of the blood
Osmoregulation - The control of the concentration of water in the blood
Sensors in the hypothalamus detect the water content in the blood. If the water content in the blood is too low, ADH (antidiuretic hormone) is released into the blood. When this reaches the kidneys, the ADH makes the walls of the collecting ducts more permeable to water molecules, so more water molecules move out via osmosis due to the water potential gradient.
If the concentration of water in the blood is too high, less ADH is released into the blood. The walls of the collecting duct become less permeable to water and so urine becomes more dilute.
2.76 Recall that urine contains water, urea and salts.
2.77 Understand that organisms are able to respond to changes in their environment
Living organisms are sensitive - they can recognise and respond to changes in external and internal environments
2.78 Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis
2.79 Understand that a coordinated response requires a stimulus, a receptor and an effector
Stimulus - a change in conditions
Receptor - An organ that recognises the stimulus
Effector - An organ which produces a response
2.80 Understand that plants respond to stimuli
Plants generally respond to stimuli by changing the way they grow - this is called a tropism
2.81 Describe the geotropic responses of roots and stems
Stems grow against gravity, therefore experiencing a negative geotropism
Roots grow in the direction of gravity for the moisture of the soil, therefore experiencing a positive geotropism. When roots are pointing straight down, all sides of the root receive the same amount of auxin so all cells elongate by the same amount. When roots are growing at an angle, gravity forces auxin to diffuse to the underside of the root, which reduces the amount of elongation on this side until the roots are in line with the force of gravity.
2.82 Describe positive phototropism of stems
If all sides of a stem receive the same amount of light, equal amounts of auxin diffuse down all sides of the shoot, so all cells around the shoot are stimulated to grow/elongate (not more cells) the same amount, so the stem will grow upwards.
If one side of a stem receives more light than the other, the auxin will diffuse to the shaded side of the stem, causing this shaded side to grow more than the side in light so the stem will curve towards the light
2.83 Describe how responses can be controlled by nervous or by hormonal communication and understand the differences between the two systems
In the nervous system, communication occurs via electrical impulses and responses are often very rapid. The hormonal/endocrine system uses chemical communication by means of hormones, which act upon target cells in other tissues and organs. This system helps to maintain basic bodily functions. Its responses are much more long term and are often less rapid than the nervous system.
2.84 Recall that the central nervous system consists of the brain and spinal cord and is linked to sense organs by nerves
Central Nervous System = Brain and Spinal Cord
2.85 Understand that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses
Stimulus → Receptor → Central nervous system → Effector → Response
→ = nerve/neurone
2.86 Describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object
Hot object (stimulus) → Pain receptor in skin → Sensory neurone → Relay neurone in CNS (spine) → Motor neurone → Biceps muscle (effector) → Hand moves (response)
2.87 Describe the structure and function of the eye as a receptor
The eye is the sense organ that responds to changes in light. The back of the eye is the retina, which contains light sensitive receptor cell. The fovea is the most sensitive part of the retina. The optic nerve is the sensory neurone for the eye and carries electrical impulses to the brain. The blind spot is where the optic nerve attaches to the retina and there are no light-sensitive cells. The lens helps focus the image and is held in place by suspensory ligaments and ciliary muscle. The pupil is the hole in the centre of the iris to let light in. The iris controls the amount of light entering the eye. The cornea is transparent and protective at the front of the eye. The sclera is a protective coating around the eye. The vitreous humour keeps the eyeball in shape.
Light-sensitive cells include cone cells, which respond to wavelength of light i.e. colour. Cone cells are clustered around the fovea. They also include rod cells, which respond to light intensity, giving us black and white images. Rod cells are found all over the retina.
2.88 Understand the function of the eye in focusing near and distant objects, and in responding to changes in light intensity
LIGHT INTENSITY
In bright light, the circular muscles contract and the radial muscles relax. The pupil constricts
In dim light, the circular muscles relax and the radial muscles contract. The pupil dilates
FOCUS
Focusing on distant objects, ciliary muscles relax and suspensory ligaments pulled tight to make the lens thin and wide, to reduce refraction as light rays are almost parallel
Focusing on nearby objects, ciliary muscles contract and suspensory ligaments slack, reducing tension on the lens which allows it to bulge, to refract light more
2.89 Describe the role of the skin in temperature regulation, with reference to sweating, vasoconstriction and vasodilation
Sweat is released on to the surface of the skin. The evaporation of this sweat needs heat energy, which it takes from the skin thus cooling the body down.
If you are hot, vasodilation will occur; blood will travel in capillaries closer to the skin and these capillaries will get wider so more heat energy from the blood will be radiated from the skin
I you are cold, vasoconstriction will occur; blood will travel through deeper vessels, which will be thinner preventing heat loss through radiation.
Shivering may occur - rapid small contractions, which require energy from respiration, releasing heat energy at the same time. Body hair may be raised on the skin by hair erector muscles to trap a layer of warm air around the skin
2.90 Understand the sources, roles and effects of the following hormones: ADH, adrenaline, insulin, testosterone, progesterone and oestrogen.
ADH - Produced in pituitary gland - causes the walls of the collecting duct to beome more/less permeable to water depending on water levels in the blood.
Insulin - Produced in the pancreas - Controls blood sugar levels - It converts excess glucose into glycogen, which is insoluble and stored in the liver. When there is not enough glucose in the blood, the pancreas secretes glucagon which turns glycogen back into glucose
Adrenaline - Produced in the adrenal glands - Prepares the body for fight or flight, the crucial moment when an animal decide whether to fight or run for its life. Some of the effects of adrenaline are faster pulse, increased sweating, hair standing on end (to appear larger), paling of the skin (blood shunting)
Testosterone - Secreted in the testes - Male sex hormone, which causes secondary sexual characteristics in boys and is needed for the production of sperm.
Progesterone and Oestrogen - Oestrogen is responsible for secondary sexual characteristics in girls and together with progesterone it controls the menstrual cycle.