B2- topic 2

HideShow resource information

Aerobic Respiration

Respiration is a series of reactions occuring in all living cells in which glucose is broken down to release energy (energy from broken down food molecules)

During Aerobic repiration oxygen is used to release energy from molecules e.g. glucose.

Glucose + oxygen ---------> carbon dioxide + water

Glucose and oxygen carried around the body into tissues by the blood. However carbon dioxide is carried through the blood as waste. These substances move through the blood through tiny blood vessels called capillaries by diffusion.

Diffusion is when particles of a substance spread out and move from one area which has a high concentration to another which has a low concetration. They diffuse down a concentration gradient.

1 of 8

Aerobic Respiration continued

Gas exchange

The tissue in the lungs are particularly spongy which has a larger surface area so more oxygen can enter the lungs through the bloodstream and  are full of tiny sacs (alveoli). These sacs are surronded by capillaries,

Oxygen that enters the body through the lungs moves into the blood through diffusion.

Carbon dioxide also leaves the blood by diffusion into the air spaces. As one gas eneters the other leaves- this is called gas exchange.

2 of 8

Anaerobic repiration

When exercising muscles use up glucose and oxygen very quickly so the blood supply to the muscles increase.

When doing a great deal of exercise, our bodies cannot supply oxygen to out muscles quickly enough. When this occurs another process to break down glucose and release energy that doesn't rely on oxygen starts to happen with aerobic respiration- anaerobic respiration

anaerobic respiration releases less energy than aerobic respiration.

cardiac output= stroke volume x heart rate

CO=volume of blood circulated by heart in a given time.

SV= volume pumped out of heart on each beat.

Anaerobic Respiration Equation:

Glucose ---------> lactic acid (broken down using oxygen into CO2 and H20)

3 of 8


Starch made of glucose molecules (thousands) joining together. When broken down in digestion, glucose is released which is used for respiration.

Plants make their own glucose using simple raw materials of carbon dioxide and water. This is photosynthesis. They can store glucose as carbohydrates, e.g. starch.

carbon dioxide + water -------> glucose + oxygen

Photosynthesis occurs in chloroplasts. Light energy (Sun) for photosynthesis is used and is absorbed by a green substance known as chlorophyll. Chlorophyll transfers light enrgy into stored chemical energy in the form of glucose.

4 of 8

Photosynthesis continued

Leaves are broad and flat (large surface area) allowing them to absorb as much light energy as they can.

Undernearth they have microscopic pores called stomata which open when in contact with light.

Pores let CO2 in the atmosphere to diffuse into the leaf, oxygen produced by cells diffuse from the inside out to the atmosphere.

 To protect the leaf without blocking out light Palisade cell layer at top of leaf to absorb more light Spongy layer.

Air spaces allow carbon dioxide to diffuse through the leaf, and increase the surface area Palisade cells contain many chloroplasts which absorbs all the available light.

The air spaces found within the leaf give the cells a large surface area to volume ratio for effective gas exchange.

5 of 8

Limiting factors

Limiting factor; a single factor that when in short supply can limit the rate of a process e.g photosynthesis

These factors include:

  • tempreture
  • Carbon dioxide concentration
  • light intensity

Increase in temperature also raises the rate of photosynthesis. However as the temperature goes over 45 degrees the enzymes start to denature and the rate falls to 0.

A plant which is grown with lots of co2 and water but with dim light will photosynthesise slowly, as increasing the amount of water and co2 will not increase photosynthesis, only increasing light will increase the rate- this is a limiting factor.

6 of 8

Water Transport

Roots absorb minerals water and mineral salts from the soil.

The surface roots contain speciallised root hair cells with long thin extensions that reach in the surronding soil.

The water enters the root hair cell by osmosis.This process is when water moves across a partially permeable membrane(a membrane which only allows certain sunstances through) from a region where water is in higher concentration to an area with low concentration.

The water moves by diffusion.

Roots can take in nitrates and other mineral ions dissolved in the soil water even if the concentration is higher in plant than soil water.

When the water and minerals have entered  the root cells they need to get to all the plants tissue. plants have speciallised tissue called xylem to transport water & dissolved minerals salts. xylem tissue have long cells which die and form hollow tube which supports the plants.

7 of 8

Water Transport continued

Glucose is made in the leaves by photosynthesis and is transformed to sucrose and transported to other parts of the plant by strands of living phloem tissue


xylem moves water and solutes from the roots to the leaves – phloem moves food substances from leaves to the rest of the plant

Water evaporates from the surface of the cells inside a leaf moves out by diffusion when the stomata is open- transpiration

8 of 8


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Cells, tissues and organs resources »