Transport Systems (Edexcel IGCSE Biology)

False.

Diffusion alone is too slow to meet the needs of multicellular organisms, which generally have high metabolic requirements

The phloem are vessels, or tubes, that transport sucrose and amino acids in plants.

False.

Movement in the phloem can occur in any direction depending on where substances are being produced or stored.

The phloem transports materials from the parts of plants where they are produced or stored, to the parts of plants where they are needed, e.g.

• From the photosynthesising leaves to the rest of the plant

• From a storage organ to newly developing leaves

True.

Phloem and xylem together make up the vascular tissue in plants. This vascular tissue is the plant transport system.

False.

Sugars are transported in the form of sucrose within the phloem.

Xylem are vessels, or tubes, that transport water and mineral ions in plants.

False.

Xylem vessels transport water and mineral ions. Sugars are transported in the phloem.

Xylem transport always occurs from the roots, upwards to the rest of the plant.

True.

Minerals are transported from the soil, into the roots and upwards in the xylem.

Xylem vessels are essential to plant survival because they transport water which is needed for photosynthesis, as well as mineral ions which are needed to build molecules, e.g. chlorophyll and amino acids

Root hair cells are adapted for absorption as follows:

• They have a large surface area

• They contain mitochondria which release energy for active transport

False.

Mineral ions move into root hair cells by active transport. Only water can move by osmosis.

Root hair cells need energy to fuel the active transport of mineral ions from the soil against a concentration gradient.

Water moves into root hair cells by osmosis due to the water concentration gradient between the soil and the cell cytoplasm. Minerals, and other dissolved substances, in the cytoplasm of root hair cells lower the water concentration, so water moves into the cells by osmosis.

Transpiration is the loss of water vapour from the leaves of plants by evaporation.

The spongy mesophyll cells are involved in transpiration as follows:

• water vapour evaporates from the surface of spongy mesophyll cells and enters the leaf air spaces

• water vapour diffuses from the leaf air spaces out of the leaf

True.

Guard cells can cause the stomata to close, preventing water vapour from exiting the leaf and stopping transpiration.

False.

Transpiration involves the loss of water from the xylem of plants, so does not affect sucrose and amino acids, which are transported in the phloem.

Water vapour exits the leaf air spaces by the process of diffusion.

Four factors that affect the rate of transpiration are:

• Humidity

• Wind speed / air movement

• Temperature

• Light intensity

As light intensity increases, the transpiration rate increases.

False.

Transpiration rate increases with light intensity because the stomata open at high light intensities to enable gas exchange for photosynthesis.

As temperature decreases the transpiration rate decreases.

True.

At higher temperatures water molecules have more kinetic energy and are more likely to diffuse out via the stomata.

True.

As wind speed increases the transpiration rate increases.

Transpiration is faster on a windy day because wind blows water vapour away from the surface of leaves, maintaining a water vapour concentration gradient between the inside and the outside of leaves.

Putting a plant inside a plastic bag will decrease its rate of transpiration. This is because the bag will trap water vapour and raise humidity levels, decreasing the water vapour concentration gradient between the leaf and the surrounding air.

False.

Increasing humidity levels will decrease the rate of transpiration. This is because humid conditions decrease the water vapour concentration gradient between the inside and the outside of the leaf.

The water vapour concentration gradient is the difference in water vapour concentration between the inside and the outside of a leaf.

The piece of equipment used to measure transpiration rate in a plant shoot is known as a potometer.

A bubble potometer works to measure transpiration rate as follows:

• A bubble is introduced into a tube containing a cut plant stem

• As the plant transpires water is pulled up the stem, causing the bubble to move

• The distance the bubble moves in a given time indicates the transpiration rate

An airtight potometer system can be ensured by:

• A potometer can be set up underwater to prevent entry of air bubbles

• Petroleum jelly can be used to seal any joins

The C of CORMMS stands for change. When investigating the effect of air movement on transpiration rate the variable that is changed is the speed of the air movement, e.g. no air movement, low air movement, high air movement.

This is part of the CORMMS criteria for planning an investigation.

Altering the position of a lamp in relation to a potometer allows the effect of light intensity on transpiration rate to be investigated.

The effect of air movement on transpiration rate can be investigated by setting up a fan or hairdryer blowing air over the plant shoot.

True.

The effect of humidity on rate of transpiration can be assessed by enclosing the plant shoot in a plastic bag. Any water vapour lost by transpiration will be trapped, raising the humidity inside the bag.

Environmental variables that should be kept the same when investigating the effect of temperature on transpiration rate include:

• Air movement

• Light intensity

• Humidity

This is part of the CORMMS criteria for planning an investigation.

Transpiration rate can be calculated as follows:

Transpiration rate = distance moved by bubble ÷ time

The O of CORMMS stands for organism. When investigating the effect of humidity on the rate of transpiration this could be:

• Same species of plant

• Same age of plant shoot

• Same number of leaves present on plant shoot

This is part of the CORMMS criteria for planning an investigation.

Plasma, which constitutes over half of the blood volume.

The main components of blood are:

• Red blood cells

• White blood cells

• Platelets

• Plasma

The primary function of red blood cells is to transport oxygen (via haemoglobin).

White blood cells are primarily involved in the immune response and defence against pathogens.

Platelets play a crucial role in blood clotting and wound healing.

Plasma helps maintain blood pressure (and transports nutrients, hormones, and waste products).

Platelets are primarily responsible for blood clotting.

Plasma transports various substances such as carbon dioxide, digested food, mineral ions, urea, hormones, and heat energy.

Carbon dioxide is dissolved in plasma as hydrogen carbonate ions and transported from respiring cells to the lungs.

Digested foods e.g. glucose and amino acids are absorbed from the small intestine and transported in plasma to cells around the body.

Plasma transports urea, a waste substance produced in the breakdown of proteins by the liver, to the kidneys.

Hormones, chemical messengers released by endocrine organs, are transported in plasma and delivered to target tissues/organs.

Heat energy released during respiration is transferred by plasma to cooler parts of the body or to the skin for dissipation.

Red blood cells transport oxygen to respiring cells.

Haemoglobin, a protein in red blood cells, binds to oxygen.

Red blood cells lack a nucleus to create more space for haemoglobin, allowing for more efficient oxygen transport.

The shape of red blood cells is described as a "biconcave disc," providing a large surface area to volume ratio for efficient oxygen diffusion.

The biconcave shape provides a large surface area to volume ratio, maximising the diffusion of oxygen in and out of the cell.

White blood cells are part of the body's immune system and defend against pathogenic microorganisms.

The two main types of white blood cells are phagocytes and lymphocytes.

Phagocytes engulf and digest pathogens through phagocytosis.

Be careful not to use the work "eat" in place of engulf.

Lymphocytes produce antibodies, which are proteins that bind to specific antigens on pathogens, and antitoxins to neutralise toxins released by pathogens.

Antibodies attach to antigens on pathogens, binding the pathogens together, preventing them from moving, and signalling phagocytes to destroy them.

Antitoxins neutralise toxins released by pathogens, preventing them from causing harm to the body.

False.

The body's response to infection involves antibodies recognising antigens.

Immunity is having sufficient levels of antibodies to protect the body from a particular disease, preventing the individual from suffering from the disease or its symptoms.

• An antigen is a protein molecule found on the surface of a cell, usually a pathogen

• An antibody is a protein produced by lymphocytes that binds to specific antigens on pathogens, causing their destruction

• An antitoxin is a protein that neutralises toxins released by pathogens

False.

Phagocytes carry out phagocytosis and engulf pathogens and other foreign molecules. They do not produce antibodies.

Vaccines are used to induce immunity to infectious diseases by introducing harmless versions of pathogens into the body.

Scientists ensure that vaccines contain harmless pathogens by killing the pathogen, making it unable to grow or divide, or using fragments of pathogens rather than whole cells.

Lymphocytes recognise the antigens and produce specific antibodies to the antigen in the vaccine.

Vaccination triggers a response where memory cells and antibodies remain in the bloodstream. Future infections by the same pathogen result in a faster immune response, preventing disease.

Vaccines also reduce the likelihood of infected individuals spreading the pathogen to others within the population, contributing to herd immunity.

Memory cells are produced after infection or vaccination and enable future antibody production to the same pathogen/antigen to occur sooner, faster and in greater quantity.

Three methods of administering vaccines are:

• orally (mouth)

• nasally (nose)

• injection

Platelets are involved in helping the blood clot and forming scabs when the skin is broken or wounded.

False.

Soluble fibrinogen proteins are converted to insoluble fibrin proteins during the blood clotting process.

Fibrin forms an insoluble mesh across the wound, trapping red blood cells to form a clot, which eventually dries to become a scab.

Blood clotting prevents significant blood loss from wounds and seals them with a scab, preventing entry of microorganisms that could cause infection until new skin grows underneath.

Platelets are fragments of cells that are involved in blood clotting and forming scabs where the skin has been cut or punctured.

The heart is a double pump that circulates oxygenated blood from the lungs to the rest of the body (systemic circuit) and deoxygenated blood from the body to the lungs (pulmonary circuit).

Deoxygenated blood from the body:

1. Enters the right atrium through the vena cava

2. Flows through the tricuspid valve into the right ventricle

3. Is pumped through the pulmonary semilunar valve into the pulmonary artery

4. To the lungs for oxygenation

The septum separates the left and right sides of the heart, preventing oxygenated and deoxygenated blood from mixing.

The left ventricle has a thicker muscle wall so that it can pump oxygenated blood at high pressure throughout the body (systemic circuit), while the right ventricle pumps deoxygenated blood at lower pressure to the lungs (pulmonary circuit).

Valves in the heart prevent the backflow of blood, ensuring that blood flows in only one direction through the heart chambers and vessels.

Oxygenated blood returns from the lungs to the heart via the pulmonary veins.

The coronary arteries supply the cardiac muscle tissue of the heart with oxygenated blood, ensuring it receives a constant supply of oxygen and glucose for aerobic respiration to release energy for muscle contraction.

The heart maintains low pressure in the pulmonary circuit, preventing damage to the capillaries in the lungs during blood circulation.

False.

Deoxygenated blood enters the right side of the heart from the body.

True.

The right ventricle muscle wall is thinner than the left ventricle muscle wall.

The pulmonary vein is the only vein to carry oxygenated blood, returning blood to the heart after gas exchange has taken place.

Heart rate is measured by counting the number of times the heart beats in a minute (bpm).

Heart rate can be influenced by factors such as hormones like adrenaline, exercise intensity, and the body's demand for oxygen and glucose.

During exercise, the heart rate increases to deliver more oxygen and glucose to the muscles, remove waste products, and meet the increased demand for energy release through respiring cells.

The heart rate remains elevated after exercise because extra oxygen is required in the muscles to break down lactic acid from anaerobic respiration, and this is how the oxygen debt is paid off. The elevated heart rate ensures extra oxygen is transported to the cells.

Recovery time is the time taken for the heart rate to return to its resting rate after exercise.

Adrenaline is a hormone that increases heart rate.

False.

During exercise respiration in the muscle cells increases.

The hormone adrenaline influences heart rate by increasing heart rate.

The coronary arteries supply the heart with oxygenated blood, delivering oxygen and glucose while removing waste products such as carbon dioxide.

CHD stands for coronary heart disease.

Coronary heart disease (CHD) occurs when fatty deposits (plaque) build up inside the coronary arteries, reducing blood flow and depriving the heart muscle of oxygen.

Plaque buildup narrows the arteries, reducing blood flow and causing a lack of oxygen to the heart muscle. This can lead to angina (chest pain) or a heart attack.

False.

Smoking is a risk factor for coronary heart disease.

High blood pressure increases the force of the blood against the coronary artery walls and consequently leads to damage of the vessels.

Four risk factors for CHD are:

• Smoking

• High blood pressure

• Obesity

• High cholesterol

True.

High cholesterol is a risk factor for CHD because it leads to a build-up of fatty deposits in the coronary arteries.

The three main types of blood vessel are arteries, veins, and capillaries.

Arteries carry blood at high pressure away from the heart.

Arteries have thick muscular walls containing elastic fibres to withstand high blood pressure and maintain it as the blood recoils. They also have a narrow lumen to help maintain high blood pressure.

Veins carry blood at low pressure towards the heart.

Veins have thin walls and a large lumen to reduce resistance to blood flow under low pressure. They also contain valves to prevent backflow of blood.

Valves prevent the back-flow of blood in the veins where blood travels under low-pressure.

Capillaries carry blood at low pressure within tissues, have walls that are one cell thick, and allow substances to easily diffuse in and out through their 'leaky' walls.

The circulatory system consists of a double pump within a closed network of blood vessels connected to the heart, responsible for transporting oxygenated blood to the body cells and returning deoxygenated blood to the heart.

The blood vessel carrying blood to the liver is the hepatic artery.

False.

The renal vein carries deoxygenated blood away from the kidneys.

The blood vessel that carries deoxygenated blood to the lungs from the heart is the pulmonary artery.

False.

The pulmonary vein carries oxygenated blood to the heart from the lungs.