AQA GCSE Biology - Autumn Term Assessment 1 2022 - Photosynthesis, Organisation and the Heart

What organisms perform photosynthesis?

Plants, algae, and some bacteria

Where does photosynthesis occur?

chloroplasts (plant cells) in the leaves

What molecules are required for photosynthesis?

carbon dioxide and water

What are the products of photosynthesis?

glucose and oxygen

Photosynthesis is

Conversion of light energy from the sun into chemical energy.

Photosynthesis formula...

6CO2 + 6H2O (+ sunlight) ---> C6 H12 O6 + 6O2

What mineral ions are needed for photosynthesis?

phosphorus, potassium, magnesium, nitrogen

Uses of glucose produced in photosynthesis

Fats and lipids (stored in seeds), proteins, starch stored in plants, to make cellulose, used for energy in respiration

Photosynthesis: endo or exothermic reaction?

Endothermic, because it takes in energy from the environment, and does not release it

Guard cells are....

- Bean shaped cells surrounding the stomatal pore in pairs that regulate the opening and closing of the stomata
- They have a thin outer wall, thick inner wall, nucleus, chloroplasts and a central vacuole

Describe the opening and closing of the stomata

When there is surplus water:
- Water moves into the guard cells by osmosis (from low to high concentration down the concentration gradient)
- Guard cells become turgid
- Stomata opens
When water is scarce:
- Water moves out of the guard cells by osmosis (from low to high concentration down the concentration gradient)
- Guard cells become flaccid
- Stomata closes

Gas Movement in the leaf

- Carbon Dioxide diffuses down the concentration gradient from a region of high concentration (outside the leaf) to a region of low concentration (inside the leaf)
- Oxygen produced in photosynthesis diffuses down the concentration gradient from an area of high concentration (inside the leaf) to a low concentration (outside the leaf)

Factors affecting the rate of photosynthesis:

light intensity, temperature, carbon dioxide concentration and the number of chloroplasts

How does temperature affect the rate of photosynthesis?

- The higher the temperature, the higher the rate of photosynthesis as the particles have more kinetic energy
- Increases the rate of successful collisions between the enzymes and the substrates and the rate of diffusion of gases
- Results in the formation of products
- If the temperature is over around 45 degrees Celsius, the enzymes may become denatured and that reduces the overall rate until it stops completely

How does light intensity affect the rate of photosynthesis?

- The higher the light intensity, the higher the rate of photosynthesis
- The rate will carry on increasing until another factor becomes the limiting factor, the graph levels off and the rate becomes constant

Calculating light intensity

Light intensity = 1/distance^2

Limiting Factor

- Can be defined as something present in the environment in such a short supply that it restricts life processes
- Doesn't end the reaction: it just stops the reaction rate from getting any faster

How does CO2 concentration affect the rate of photosynthesis?

- The higher the concentration of CO2, the higher the rate of photosynthesis
- The rate will carry on increasing until another factor becomes the limiting factor, the graph levels off and the rate becomes constant

How does the number of chloroplasts affect the rate of photosynthesis?

- The more chloroplasts the plant has, the faster the rate of photosynthesis
- This is because they contain the green pigment chlorophyll which absorbs light energy for photosynthesis

How is the leaf adapted for photosynthesis? (6 marks)

- Waxy cuticle coats the leaf and prevents water loss as it is waterproof and gas-proof, and transparent which means it can absorb sunlight faster
- Upper epidermis which protects inner tissues and reduces water loss because it is a thin transparent layer that allows light for photosynthesis and isn't reflected away and does not have any air spaces or pores so no gas/water is lost
- Palisade mesophyll, it's the main site of photosynthesis as glucose is made here, and this is possible as it has many chloroplasts that are filled with chlorophyll and are located near the top of the leaf so it has more access to sunlight and they are tightly packed long and thin cells, and so have more surface area
- Spongy mesophyll, which is responsible for gas exchange, allows gas to pass through the large air spaces between and has a large surface area to enable rapid diffusion of gases
- Lower epidermis, which protects the inner tissues and allows light for photosynthesis as it is a thin and transparent layer and has pores called stomata
- Stomata, located mainly in the lower epidermis to prevent water loss, are where the gases go in and out of the leaf, and are controlled by guard cells to allow for CO2 to diffuse in and O2 and water vapour to diffuse out of the leaf, and prevents water loss by closing

Xylem

Dead cells in the vascular tissue/bundle that carries water upward from the roots to every part of a plant (transpiration). water only moves upward

Phloem

Living cells that transport sugar and other molecules made by the plant in the leaf to the rest of the plant (translocation). sugar moves in both directions

Properties of xylem

Form long, dead hollow vessels, have no end walls so stream of water is continuous, strengthened by lignin which is also waterproof as it causes cells to die, have no internal organelles so allows for a larger capacity of water to be carried

Properties of phloem

Have sieve plates that distribute amino acids evenly throughout the plant, have no nuclei, have perforated end plates so that their cytoplasm connects one cell to the next, have companion cells which have nuclei, cytoplasm and many mitochondria which provide energy

Route of water from soil to roots

Water is absorbed by the roots from the soil: it moves from a lower to a higher concentration by osmosis into the root hair cell

Route of mineral ions from soil to roots

Mineral ions like magnesium enter the plant through the roots, and as they move from an area of lower concentration in the soil to higher concentration in the plant, they move against the concentration gradient via active transport

Adaptations of root hair cells

- Have extensions which give them a larger surface area so the rate of water moving into the plant by osmosis is higher
- Have many mitochondria which provide energy for active transport for the absorption of mineral ions in the soil
- They don't have chloroplasts as they are underground and don't need to photosynthesise, which means they have more space for a large vacuole which maintains the concentration gradient for water to move into the plant

Turgid

swollen as from a fluid (often water in a plant)

Flaccid

not plump and swollen but floppy or loose (often due to lack of water in a plant)

Stomatal Density

number of stomata per unit area

Uses of water in a plant

Reactant for photosynthesis, movement of mineral ions and for support and frigidity

Movement of water from roots to rest of plant

- Water moves from the soil into the roots by osmosis
- The water moves from the roots into the stem, and this replaces the water that is constantly moving up the stem
- Water moves up the stem into the leaf to replace water lost by transpiration
- Water is lost from the leaves through open pores (stomata) by transpiration

Transpiration

Loss of water vapour by evaporation from the leaves of a plant through the stomata

Transpiration stream

the movement of water through a plant from the roots to leaves as a result of loss of water by evaporation from the surface of the leaves

Adaptations to limit water loss in a plant

- Waterproof waxy cuticle
- stomata closing at night
- more stomata on the underlayer (most plants)
- wilting
- guard cells

Adaptations to limit water loss in aquatic plants

- Stomata on upper layer to allow CO2 uptake from the atmosphere
- No need for roots and xylem (no need for lignin) as leaf is supported by water
- Very thin cuticle, since water conservation is not a problem

Adaptations to limit water loss in desert plants

- Leaves reduced to spines to reduce surface area for water loss (and deter grazing animals)
- Sunken stomata (in grooves) to avoid drying winds and trap water vapour
- Very thick waxy cuticle which is waterproof
- Shallow roots to absorb water from lightest rainfall
- Very deep roots penetrate to the very low water table
- Often have hairs to prevent water loss by trapping moist air

Potometer

a device used for measuring the rate of water uptake of a plant due to photosynthesis and transpiration

Rate of transpiration

Rate of loss of water through the stomata on leaves

Calculating the rate of transpiration using a bubble potometer

- Measure distance the air bubble travels
- Time how long it takes to travel that distance
- Rate = Distance/ Time

Factors affecting the rate of transpiration

- Temperature
- Ventilation/ air movement
- Humidity
- Light

How does temperature affect the rate of transpiration?

- The higher the temperature, the higher the rate of transpiration
- Particles have more kinetic energy and so more stomata open and diffusion occurs more rapidly

How does ventilation/ air movement affect the rate of transpiration?

- The higher the wind velocity, the higher the rate of transpiration
- This is because it helps to remove the boundary layer of water molecules surrounding the leaf
- Increases the water concentration gradient, so osmosis occurs more rapidly

How does humidity affect the rate of transpiration?

- The higher the humidity, the lower the rate of transpiration
- It increases the number of water molecules surrounding the leaf and decreases the water concentration gradient of water between the inside and outside of the plant so osmosis occurs less rapidly

How does light intensity affect the rate of transpiration?

- The higher the light intensity, the higher the rate of transpiration
- This is because the plant is essentially photosynthesizing more, so more stomata open and more water is lost

Atria

the two upper chambers of the heart

Ventricles

the two lower chambers of the heart

Aorta

Largest artery in the body that takes oxygenated blood from the heart to the rest of the body

Vena cava

largest vein in the body that takes deoxygenated blood from the body to the heart

Pulmonary artery

artery carrying deoxygenated blood from the heart to the lungs

Pulmonary vein

vein carrying oxygenated blood from the lungs to the heart

Describe the movement of gases in the lungs during gas exchange

- There is more CO2 in the blood than in the alveolus so CO2 diffuses into the alveolus and is breathed out
- There is more oxygen in the alveolus than in the blood so oxygen diffuses into the blood and is transported to the body cells

Features of the lungs for efficient gas exchange

- Constant ventilation (movement of air being breathed in and out)
- Many alveoli which are small and packed into the lungs so they have a large total surface area
- Good blood supply (blood vessels)
- Thin walls for gas exchange (1 cell thick)

Properties of a single circulatory system

- Blood flows once through the heart in 1 cycle through 1 circuit called the systemic circuit
- Occurs in fish and reptiles
- Heart has only 2 chambers
- Only deoxygenated blood passes through the heart
- Less efficient as the gill capillaries slow down blood flow, the body receives blood at low pressure which decreases the rate of oxygen supply to the cells

Properties of a double circulatory system

- Blood flows twice through the heart in 1 cycle through 2 circuits called the pulmonary and systemic circuits
- Occurs in all other vertebrates
- Heart has 4 chambers
Both deoxygenated and oxygenated blood passes through the heart and are kept separate which is more efficient
- More efficient as blood is at a higher pressure (especially in humans and mammals which increases the rate of supply of glucose and oxygen to the cell and also rapid removal of wastes from them

The Pulmonary Circuit

Consists of
- The pulmonary artery which takes deoxygenated blood from the right ventricle of the heart to the lungs to be oxygenated
- The pulmonary vein which takes oxygenated blood from the lungs to the left atrium of the heart to be pumped around the body

The Systemic Circuit

Consists of
- The aorta (the largest artery) which takes oxygenated blood from the left ventricle of the heart to be pumped around the body, and splits into the hepatic artery (blood to liver), the mesenteric artery (blood to guts), and the renal artery (blood to kidneys)
- The vena cava (the largest vein) which takes deoxygenated blood from the body to the right atrium of the heart to be pumped to the lungs and consists of the hepatic portal vein (blood from gut to liver), the renal vein (blood from kidneys to heart), and the hepatic vein (blood from liver to heart)

Describe the blood flow through the heart

- Deoxygenated blood enters the heart from the vena cava into the right atrium
- Blood flows into right ventricle through the right AV valve
- Blood leaves the heart via the pulmonary artery to the lungs to be oxygenated
- Blood flows through the capillaries around the lungs and oxygen diffuses into the blood and CO2 diffuses out
- The oxygenated blood enters the left atrium via the pulmonary vein
- Blood flows into the left ventricle through the left AV valve
- Blood leaves the heart via the aorta and flows around the body

Arteries

Blood vessels that carry blood away from the heart

Veins

Blood vessels that carry blood back to the heart (visit the heart)

Capillaries

Connect veins and arteries

Movement of blood through blood vessels

- Heart pumps blood around the body
- Arteries carry the blood from the heart to the capillaries
- Arteries split up to make capillaries
- The capillaries go to every cell in the body
- The capillaries join to make veins
- Veins have valves to keep blood flowing in the right direction
- The veins carry blood from the capillaries back to the heart

Properties of Arteries and Arterioles

- Carry oxygenated blood at high pressure as the lumen is narrow
- Blood is carried away from the heart to the body (except the pulmonary artery)
- Small lumen keeps the pressure high
- Thick layer of muscle and elastic tissue allows the arteries to stretch as blood flows through
- Structure from inside to out is lumen, tunica interna, tunical media and tunica externa
- tend to be

Lumen

Gap in the middle of any tube

Properties of Veins and Venules

- Carry deoxygenated blood at lower pressure from the body to the heart (apart from the pulmonary vein)
- The blood in the vein is a darker red colour as it is deoxygenated, not blue!
- Have wide and long lumen which allows for large volumes of blood to flow easily
- Have valves which remove the backflow of blood
- Veins have less elastic and muscle tissue than arteries
- Structure from inside to out is lumen, tunica interna, tunical media and tunica externa
- Tend to be

Properties of capillaries

- They are small blood vessels which link arteries and veins
- Large networks of them surround organs which give them a large surface area and blood travels through them very slowly, allowing substances to diffuse in and out of the blood
- Walls are only one cell thick so there is a shorter distance for the gases to travel and no cell in your body is ever more than 0.05mm away from a capillary
- Have small lumen (slows the flow of blood for successful gas exchange)
- Most famous are the ones in the lungs around the alveoli

Erythrocytes

another name for red blood cells

Leukocytes

white blood cells

Properties of blood plasma

- A yellowish colored liquid component of blood that forms about 55% of your blood
- Bathes the cells and transports many substances
- Carries CO2 produced in body cells back to lungs
- Carries urea from the liver to the kidneys for excretion
- Carries solubles products of digestion absorbed by the villi in the small intestines to body cells (such as amino acids)
- Carries lactic acid from muscles when exercising to the liver to be oxidised
- Carries antibodies from white blood cells to the site of infection
- Carries hormones from glands to the target organs (such as thyroid glands located in the front of your neck)

Properties of platelets

- Fragments of cells that can release fibres
- When you cut your skin, they gather at the site and release fibre-like proteins which form a mesh
- As the blood flows by, the red blood cells get caught in it and dry out to form a scab/ blood clot
- They are good for the body as it is not an open wound and protects us from too much bleeding until the skin can be reformed and heal

Properties of white blood cells

- Produce antibodies (the lymphocytes do this) and antitoxins to neutralise antitoxins
- Phagocytes engulf microbes and digest them (mucus)
- Distinct due to their shape and oddly shaped nuclei (often a lot bigger than other nuclei)

Properties of red blood cells

- Transport oxygen from lungs to all somatic cells so that respiration can take place
- No nuclei so there is more space to carry haemoglobin + oxygen that binds to it
- Biconcave disc shape provides a larger SA:V ratio for diffusion of oxygen
- As haemoglobin is red (pigments are always proteins), blood is also red

Properties of haemoglobin

- Large protein molecule folded around 4 iron
- When the concentration of the oxygen is lower, in the body organs, the oxyhaemoglobin splits to release oxygen to the tissues
- If your body lacks Fe (iron), your body can't make enough red blood cells and you can suffer from anaemia which can make you feel tired, fatigued and dizzy

Systole

Contraction of the heart muscle (constricted space)

Diastole

Relaxation of the heart muscle (dilated space)

The stages of the cardiac cycle

atrial systole, ventricular systole, diastole

stage 1: atrial systole

- Heart is full of blood, the muscles are contracting in both atria and the space is constricted
- AV valves open because the pressure in the atria is increased and so the valves are forced open
- Blood flows into both ventricles, and there is no backflow from the heart as veins have valves

Stage 2: Ventricular systole, atrial diastole

- Atria relax and space is dilated in the atria
- Ventricles contract (0.1 sec after atria), space in there is constricted, and due to pressure, AV valves close
- Increase in pressure causes semilunar valves to open, and the blood flows from the ventricles to the arteries and lasts around 0.3 secs

stage 3: ventricular diastole

- Ventricles relax, space is dilated
- Because of low pressure in the heart, blood flows from veins into atria again
- Blood flows from atria to ventricles and the whole process starts again...

Pressure graph for one cycle

Coronary

pertaining to the heart

Cholesterol

LDL and HDL

Plaque

A deposit of fatty material on the inner lining of an arterial wall

CVD (cardiovascular disease)

a disease that affects the heart and blood vessels

Angina

Restricted flow of blood to the heart - lack of oxygen leads to anaerobic respiration and pain in the chest

heart attack (myocardial infarction)

Heart muscle totally starved of oxygen so it dies

Stroke

Blood supply to the brain is restricted, so it starves the brain cells of oxygen

Aneurysm

A balloon-like blood-filled structure that forms at a weak point in the artery wall. They frequently burst leading to blood loss

heart failure

A condition where the heart can't pump enough blood to meet the body's needs

Irregular heartbeat

A problem with the pacemaker cells (found in the muscle walls of the right atrium) if the heart is not contracting efficiently

Leaky/faulty valves

Valves can become leaky/faulty so the blood does not pass efficiently through the heart and can back flow

Coronary artery

Supplies the heart muscle cells with oxygen and nutrients so that it can beat continuously and keep respiring without getting tired

Coronary Heart Disease

- Occurs when fatty material builds up in the coronary arteries, narrowing them and restricting blood flow to the heart
- Can happen to any artery, but is particularly dangerous here as it is quite small

Atheroma

A fatty deposit which forms within the wall of an artery (plaque)

Atherosclerosis

The narrowing and hardening of the arteries and the narrowing of the lumen

CHD development in the vessels

- Stage 1: lumen is wide , plenty of blood flow
- Stage 2: Cluded lumen as the fat buildup restricts the blood flow to the heart, but still provides some blood to the heart (could cause angina)
- Stage 3: Platelets will get trapped and form a mesh, trap red blood cells and forma blood clot, which starved the heart of oxygen and therefore causes a heart attack

LDL cholesterol (low density lipoprotein)

- Also known as monounsaturated fats or saturated lipids, and are generally animal based
- When turned into a lipoprotein and carried by the blood, they form LDLs which are linked to increased risk of heart disease, and so are known as bad cholesterol

HDL cholesterol (high density lipoprotein)

- Also known as polyunsaturated fats or unsaturated lipids, and are generally plant-based
- When turned into a lipoprotein and carried by the blood, they form HDLs which regulate/clear LDLs and promote the excretion of them, and are linked to reduced risk of heart disease and so are known as good cholesterol

Functions of Cholesterol

- It is a waxy, fat-like substance
- Making bile (needed for digestion)
- Repair and maintenance of cell membranes
- Synthesis of steroid hormones, like testosterone and cortisone
- However it is insoluble in blood and must be carried by lipoproteins

Controlling cholesterol

The total amount of cholesterol in people's bodies is different for everyone, and mainly depends on their diet and gene