Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide.

Leaves
Leaves are adapted for photosynthesis by having a large surface area, and contain openings, called stomata to allow carbon dioxide into the leaf. Although these design features are good for photosynthesis, they can result in the leaf losing a lot of water. The cells inside the leaf have water on their surface. Some of this water evaporates, and the water vapour can then escape from inside the leaf by diffusion.
To reduce loss the leaf is coated in a wax cuticle to stop the water vapour escaping through the epidermis. Leaves usually have fewer stomata on their top surface to reduce this water loss.

Root hair cells and osmosis

Roots

Plants absorb water from the soil by osmosis. Root hair cells are adapted for this by having a large surface area to speed up osmosis.
The absorbed water is transported through the roots to the rest of the plant where it is used for different purposes:
It is a reactant used in photosynthesis
It supports leaves and shoots by keeping the cells rigid
It cools the leaves by evaporation
It transports dissolved minerals around the plan

Root - xylem and phloem in the centre of the root to withstand stretching forces.

Stem – the xylem and phloem are arranged in bundles near the edge of the stem to resist compression and bending forces.

Plant transport

No heart, no blood and no circulation, but plants do need a transport system to move food, water and minerals around. They use two different systems – xylem moves water and solutes from the roots to the leaves – phloem moves food substances from leaves to the rest of the plant. Both of these systems are rows of cells that make continuous tubes running the full length of the plant.

Transpiration

Transpiration explains how water moves up the plant against gravity in tubes made of dead xylem cells without the use of a pump.
Water on the surface of spongy and palisade cells (inside the leaf) evaporates and then diffuses out of the leaf. This is called transpiration. More water is drawn out of the xylem cells inside the leaf to replace what's lost. As the xylem cells make a continuous tube from the leaf, down the stem to the roots, this acts like a drinking straw, producing a flow of water and dissolved minerals from roots to leaves.

Transpiration

Transpiration explains how water moves up the plant against gravity in tubes made of dead xylem cells without the use of a pump.
Water on the surface of spongy and palisade cells (inside the leaf) evaporates and then diffuses out of the leaf. This is called transpiration. More water is drawn out of the xylem cells inside the leaf to replace what's lost. As the xylem cells make a continuous tube from the leaf, down the stem to the roots, this acts like a drinking straw, producing a flow of water and dissolved minerals from roots to leaves.

Maximising growth
Farmers can use their knowledge of these limiting factors to increase crop growth in greenhouses. They may use artificial light so that photosynthesis can continue beyond daylight hours, or in a higher-than-normal light intensity. The use of paraffin lamps inside a greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon dioxide, and heat too.

If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot.
If you plot the rate of photosynthesis against the levels of these three limiting factors, you get graphs like the ones above.
In practice, any one of these factors could limit the rate of photosynthesis.

Respiration supplies the body with energy. The circulatory system takes oxygen and glucose to the cells and removes waste products. We can improve our fitness by taking exercise. Anaerobic respiration occurs when there is too little oxygen present.

Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide.

Factors affecting photosynthesis

Three factors can limit the speed of photosynthesis: light intensity, carbon dioxide concentration and temperature.Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.

Features of leaves
Adaption Purpose
Large surface area To absorb more light
Thin Short distance for carbon dioxide to diffuse into leaf cells
Chlorophyll Absorbs sunlight to transfer energy into chemicals
Network of veins To support the leaf and transport water and carbohydrates
Stomata Allow carbon dioxide to diffuse into the leaf

Leaves enable photosynthesis to occur. Photosynthesis is the process by which leaves absorb light and carbon dioxide to produce carbohydrate (food) for plants to grow. Leaves are adapted to perform their function, eg they have a large surface area to absorb sunlight.
Plants have two different types of 'transport' tissue, xylem and phloem, that move substances in and around the plant. When water evaporates from the leaves, resulting in more water being drawn up from the roots, it is called transpiration.
Structure of a leaf

Functions of leaves
The function of a leaf is photosynthesis – to absorb light and carbon dioxide to produce carbohydrates. The equation for photosynthesis is:
Carbon dioxide and water → glucose and oxygen
Did you know:
Leaves are the source of all of food on the planet
Leaves recycle all of the world's carbon dioxide in the air
Leaves contain the world's most abundant enzyme

The after effect of exercise

During hard exercise when anaerobic respiration occurs with aerobic respiration, an oxygen debt builds up. This is now known as Excess Post-exercise Oxygen Debt or EPOC. This is because glucose is not broken down completely to form carbon dioxide and water. Some of it is broken down to form lactic acid. Panting after exercise provides oxygen to break down lactic acid. The increased heart rate also allows lactic acid to be carried away by the blood to the liver, where it is broken down.

Anaerobic respiration

When exercising very hard, the heart cannot get enough oxygen to the muscles. Anaerobic respiration does not need oxygen. It releases energy from glucose but the amount is much lower. It happens when there is not enough oxygen for aerobic respiration. Here is the word equation:
glucose → lactic acid (+ energy)
Much less energy is released by anaerobic respiration than by aerobic respiration. The lactic acid that forms causes muscle fatigue and pain.

Effect of exercise on breathing

During exercise, the muscle cells respire more than they do at rest. This means:
Oxygen and glucose must be delivered to them more quickly
Waste carbon dioxide must be removed more quickly
This is achieved by increasing the breathing rate and heart rate. The increase in heart rate can be detected by measuring the pulse rate. The stroke volume also increases – this is the volume of blood pumped each beat. The total cardiac output can be calculated using the equation:
Cardiac output = stroke volume x heart rate
During hard exercise, the oxygen supply may not be enough for the needs of the muscle cells. When this happens, anaerobic respiration takes place, as well as aerobic respiration.

The circulatory system
Blood carries oxygen and nutrients to the body's cells,and waste products away from them. The circulatory system consists of:
The heart, which is the muscular pump that keeps the blood moving
The arteries, which carry blood away from the heart
The veins, which return blood to the heart
The capillaries, which are tiny blood vessels that are close to the body's cells
The diagram outlines the circulatory system. Oxygenated blood is shown in red, and deoxygenated blood in blue. A process called diffusion takes place in the capillaries. Diffusion is where particles of a high concentration move to an area of low concentration. Glucose and oxygen diffuse into the cells from the capillaries. Carbon dioxide diffuses out of the cells into the blood in the capillaries.