B7: Transport

B7.1: Transport in Plants

The xylem and phloem are both tissues to transport substances throughout the plant

The xylem transports water and minerals from the roots of the plant to the leaf for photosynthesis in the mesophyll cells and transpiration in the stomata

They are made up of dead cells connected end to end
Those cells do not have a cytoplasm and does not allow water to pass through the membrane
Have thick walls strengthened by a substance called lignin

The phloem transports sucrose and amino acids throughout the plant

They contain living cells with cytoplasm
Materials are transported from the source to the storages

The phloem and xylem are found in vascular bundles (a transport system in plants) near the edge of the stem. The phloem is found on the outside, while xylem is found on the inside.

Cross section of a vascular bundle

Root hair cells

Diagram of a root hair cell

Located at ends of roots of plants
Function is to absorb waters and minerals through osmosis from the soil
Adapted to have a larger surface area so the rate of absorption will increase
Water enters the plant through osmosis into the root hair cells

Transpiration

Transpiration is the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata
The released water vapour fills the atmosphere and cools the area down (as heat energy is used to convert water into water vapour)
Helps transport minerals and water up the plant and causing the plant to keep its rigidity
Water evaporates from the surface of the spongy mesophyll and out of the stomata
Because of the gaps between the spongy mesophyll and the stomata, there is a large surface area for the water to evaporate from which leads to quicker evaporation
Evaporation happens when the stomata is open

Transport of water up the plant

Water diffuses by osmosis into the root hair cells
The water then diffuses within the plant to the root cortex cells, and then to the xylem
Water molecules are cohesive, and the loss of water vapour from transpiration creates a pull on the water in the xylem
The water in the xylem is pulled up because of the cohesive attracted forces, and goes up to the mesophyll cells in the leaves
The faster transpiration occurs, the faster water moves up the xylem

Effects of temperature and humidity and transpiration

When the temperature increases, the rate of transpiration also increases

Higher temperatures allow rates of evaporation on the surface of the mesophyll cells to be faster
This leads to more evaporation from the stomata

When the humidity increases, the rate of transpiration decreases

Osmosis occurs fastest at a larger concentration gradient
When humidity is high, the air is not dry, meaning that less water vapour would diffuse into the air
However, water vapour will diffuse faster into drier air as it has less water particles, meaning that there would be a larger concentration gradient

Translocation

Translocation is the movement of amino acids and sucrose from sources/production regions to regions to store the nutrients or use them for respiration or growth in the phloem
The phloem is made out of living cells which have sieves (small holes) at the end of the cell walls, which allows substances to flow through the cells easily
Transport in the phloem goes in different directions at different times (but amino acids and sucrose always moves from a source to a storage)

During winter, there are no leaves, and phloem transports the nutrients from the storage to the rest of the plant to continue respiration
During a period of growth for the plant (like spring), areas that store the nutrients (like the roots) transport the nutrients to the growing parts of the plant
During a period where the plant has already grown, leaves use photosynthesis to produce sugars and transports the nutrients to the roots to store them

B7.2: Transport in Mammals

It is a system of blood vessels with a pump and valves to ensure one-way flow of blood

Double Circulation

Double circulation is when blood passes through the heart twice in one cycle all around the body
The right of the heart receives blood deprived of energy from the body and transports it to the lungs (where oxygen diffuses into the red blood cells)
The left of the heart receives blood with oxygen from the lungs and transports it to the rest of the body to use

Double circulation is useful because...

When blood travels through the capillaries of the lungs, it loses the pressure that had come from the heart pumping, causing it to travel slower
However, when the blood reaches the heart for a second time, pressure can be increased once more and the blood can move faster
Therefore, cells can get their oxygen and glucose from blood to produce energy from respiration faster as well

Structure of the heart

Diagram of the heart

The septum is a muscular wall that divides the left and right side of the heart. This is to make sure that deoxygenated and oxygenated blood do not mix
The top two chambers of the heart are known as atria (singular: atrium). The left atrium receives oxygenated blood from the lungs through the pulmonary vein while the right atrium receives deoxygenated blood from the rest of the body through the superior vena cava
The veins carry blood back to the heart from other parts of the body
The bottom two chambers of the heart are known as ventricles (singular: ventricles). The right ventricle pumps out deoxygenated blood to the lungs through the pulmonary artery and the left ventricle pumps out oxygenated blood to the rest of the body through the aorta
The arteries pump blood away from the heart
The ventricles have thicker walls than the atria as they need a higher pressure to pump blood away from the heart
The left ventricle has a thicker wall than the right ventricle as it needs a higher pressure to pump to the whole of the body

There are 2 pairs of valves in the heart

The atrioventricular valves are the Tricuspid on the right of the heart and the Mitral Valve on the left of the heart. They separate atria and ventricles
When the atria contract, the atrioventricular valves open. However, when the ventricles contract, the atrioventricular valves are forced shut to prevent blood flowing back from the ventricles to the atria
The second pair are the semilunar valves which are found in the two arteries: pulmonary artery and aorta. They are the only arteries in the body with valves
When the ventricles contract, the valves open, letting blood out of the heart, and close shortly after

Main blood vessels

The main blood vessels of the heart are the...

Vena Cava: vein which transports deoxygenated blood from the rest of the body to the right atrium
Pulmonary Vein: vein which transports oxygenated blood from the lungs to the left atrium
Aorta: artery which transports deoxygenated blood from the right ventricle to the lungs
Pulmonary Artery: artery which transports oxygenated blood from the left ventricle to the rest of the body

The main blood vessels connecting to the lungs are the...

Pulmonary Vein: vein which transports oxygenated blood from the lungs to the left atrium
Aorta: artery which transports deoxygenated blood from the right ventricle to the lungs

The main blood vessels connecting to the kidney are the...

Renal Artery: an artery that branches of the aorta and brings blood to the kidney for purification
Renal Vein: a vein that returns purified blood and to the heart through the inferior vena cava

Coronary heart disease

The heart is made of muscles cells that need supplies in blood supplied by coronary arteries
When these coronary arteries are blocked up by plaques (fats), blood cannot be forced through the arteries like before, and the blood supply to the heart muscles are lessened
This causes angina, which is severe chest pains
When the blood supply is completely blocked, parts of the heart do not receive their supply of blood and cannot respire, causing heart attacks
Risk factors include of coronary heart disease...

Poor diet: Diets high in saturated fat increases blood cholesterol and chance of the buildup of fat in the coronary blood arteries
Stress: Hormones are produced when one is under stress. This increases blood pressure, and also the chance of blocking blood in the coronary blood arteries
Smoking: Nicotine makes blood vessels narrower, increasing blood pressure. This causes the buildup of fat. If this happens in the coronary artery, this causes a risk of coronary heart disease
Genetic predisposition: Those with family with a history of coronary heart disease often have an increased risk of having it as well
Age: Over age, the risk of developing coronary heart disease increases
Gender: Males are more likely to develop coronary heart disease than females

The effect of physical activity on pulse rate

Pulse rate increases with the intensity of physical activity
The blood pumps faster when the body is exercising to ensure that blood can supply nutrients and oxygen to energise the muscles that are working
The heart continues to beat quickly after exercise to remove waste products from muscle cells
Muscles may also respire anaerobically due to a lack of oxygen and may leave lactic acid in the muscles
To remove the lactic acid and replace the reserves of oxygen used up in the body, the heart beats quickly

Structure of blood vessels

Arteries

Carry blood quickly away from the heart at high pressures
Have thick muscular walls to keep a high pressure
Have a thin channel within the blood vessel to keep a high pressure
Aside from the pulmonary artery, the arteries carry oxygenated blood

Veins

Carry blood slowly towards the heart at low pressures
Aside from the pulmonary artery, the veins carry deoxygenated blood
Have thin walls and a large channel within the blood vessel
Veins contain valves which ensure that blood travels to the heart does not flow to the other direction

Capillaries

Carry both oxygenated and deoxygenated blood within tissues slowly at low pressure
Have very thin walls that are one cell wall thick to diffuse quickly

Components of blood

Blood consists of red blood cells, white blood cells, platelets, and plasma. These are the functions of these different components

red blood cells in transporting oxygen, including the role of haemoglobin
white blood cells in phagocytosis and antibody production
platelets in clotting (details are not required)
plasma in the transport of blood cells, ions, soluble nutrients, hormones and carbon dioxide

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