Respiration (GCSE)

Página 1

SUMMARY

CELLULAR RESPIRATION:

Respiration releases energy- it is an exothermic process

DON'T CONFUSE IT WITH PHOTOSYNTHESIS!!

Photosynthesis is the process by which plants (and some bacteria) synthesis food molecules which they then use for respiration, along with some other things.

Photosynthesis requires energy- making it endothermic

DON'T CONFUSE RESPIRATION WITH BREATHING- THAT IS VENTILATION. RESPIRATION OCCURS IN CELLS

Why do organisms need energy?

All organisms need energy to live. This energy is used:

to drive the chemical reactions needed to keep organisms alive – the reactions to build complex carbohydrates, proteins and lipids from the products of photosynthesis in plants, and the products of digestion in animals, require energy

movement – in animals, energy is needed to make muscles contract, while in plants, it is needed for transport of substances in the phloem

Respiration is only around 40% efficient. As animals respire, heat is also released. In birds and mammals, this heat is distributed around the body by the blood. It keeps these animals warm and helps to keep a constant internal temperature.

Energy is also used:

for cell division

to maintain constant conditions in cells and the body – homeostasis

to move molecules against concentration gradients in active transport

for the transmission of nerve impulses

Página 2

Anaerobic and Aerobic Respiration

Respiration is a series of reactions, but this summarises the overall process.

The first stages of respiration occur in the cytoplasm of cells, but most of the energy released is in the mitochondria.

Aerobic Respiration:

Respiration that uses oxygen to break down molecules is reffered to as Aerobic ( uses 'Aer' I suppose... :)) )

Glucose is the molecule that is often used in respiration. In this case, it is oxidised to release energy.

This is the WORD EQUATION: glucose + oxygen ---> Carbon dioxide + water (+ energy released)

This is the SYMBOL EQUATION: C6H12O6 + 6O2 → 6CO2 + 6H2O (+ energy released)

Anaerobic Respiration

Most organisms cannot respire without oxygen but some tissues/ organisms can continue to respire for a while without oxygen.

One very good example of this are human muscles. Our muscles can respire for a while without a supply of oxygen. this is essentially ineffective but it very useful when it comes to running away from danger- for example.

(The glucose in muscles is converted into lactic acid)

This is the WORD EQUATION: glucose ---> lactic acid (+energy released)

ANAEROBIC RESPIRATION ONLY OCCURS IN THE CYTOPLASM OF CELLS

Certain plants, and plant cells also respire anaerobically. These include plants that grow in marshes, where oxygen concentrations will be low.

Página 3

RESPONSE TO EXERCISE

Muscles need energy to contract. While exercising, the muscles need additional energy as:

the breathing rate and volume of each breath increases to bring more oxygen into the body and remove the carbon dioxide produced

the heart rate increases, to supply the muscles with extra oxygen and remove the carbon dioxide produced

If insufficient oxygen is available to the muscles, for instance the exercise is vigorous and/or prolonged, the heart and lungs are unable to supply sufficient oxygen.

Muscles begin to respire anaerobically.

Lactic acid is produced from glucose, instead of carbon dioxide and water. Muscles continue to contract, but less efficiently.

During long periods of vigorous activity:

lactic acid levels build up

glycogen reserves in the muscles become low as more glucose is used for respiration, and additional glucose is transported from the liver.

This build-up of lactic acid produces an oxygen debt.

As body stores of glycogen become low, the person suffers from muscle fatigue.