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Respiration and Photosynthesis


The process by which plants use carbon dioxide, water and light trapped by chlorophyll to make food in the form of glucose, with oxygen being given off during the process.

When does photosynthesis take place?

Photosynthesis took place when there is presence of carbon dioxide, water, sunlight and chlorophyll.

Sunlight (light energy)

  • Light energy is converted to chemical energy stored in glucose.


  • This green pigment absorbs light energy and changes it into chemical energy needed to manufacture glucose.

Carbon dioxide and water

  • These are the raw materials needed to form carbohydrates (glucose).

Suitable temperature

  • Photosynthesis depends on the reactions of enzymes in the chloroplasts. Enzyme reactions are fastest at a suitable temperature.

Where does photosynthesis take place?

Photosynthesis took place in the chloroplasts which can be found in cytoplasm of a leaf cell, it has disc‐like structures and contain the green pigments chlorophyll which traps sunlight for photosynthesis, chlorophyll also makes the plant green in colour.

How does photosynthesis take place?


The chlorophyll inside the plant cell will absorb the light, mostly the red and blue light, the green light will usually be reflected or transmitted.

When light energy is absorbed by chlorophyll and transformed into chemical energy. The chemical energy is then used in the synthesis of glucose from carbon dioxide and water. And oxygen is produced during the process.

Carbon dioxide:

Carbon dioxide is taken into the plant through the stomata.

carbon dioxide was diffused and taken in through the stomata, excess oxygen leaves the plant also through stomata by diffusion.


Water was taken in through the root of the plant, it travel up the plant through the xylem tube and was carried to every part of the plant.


Respiration took place all the time as all living cells need energy to carry out many vital processes all the time.

There are several kinds of respiration that scientist had discovered:

  • Cellular Respiration
  • Tissue Respiration
  • External Respiration
  • Aerobic Respiration
Cellular Respiration
Cellular respiration takes place in all the living cells of organisms.
During cellular respiration, the chemical energy stored in food molecules is released to living organisms.
So through cellular respiration the chemical energy which is locked up in food molecules such as glucose will be let out and use as energy.
Chemical Energy (in food) → Energy (for organisms)
Tissue Respiration
Tissue respiration is the process by which food substances are broken down in living cells.
A large amount of energy is released for the cells to perform different activities.
In tissue respiration, glucose combines with oxygen to release energy, carbon dioxide and water.
Glucose + oxygen  → carbon dioxide + water + energy
External Respiration
External respiration is the process of bringing the oxygen from the surrounding environment to the cells for tissue respiration to take place.
External respiration is also responsible for removing from the body the carbon dioxide and water formed during tissue respiration respiration.
Breathing is one of the example of external respiration.
Aerobic Respiration
Aerobic respiration is the process whereby food substances are broken down in the presence of oxygen with the release of energy in living cells. Carbon dioxide and water are released as waste products.
Aerobic respiration is important to most of the organisms, most of the organisms respire aerobically. During the process of Aerobic respiration, the energy released is used for:

  • Growth (building up of proteins)
  • Muscle contractions (e.g. heartbeats)
  • Digestion and absorption of food substances
  • Cell division
The aerobic respiration help the organisms to grow and also to pump blood, without aerobic respiration, the organisms will not be able to grow and survive.
Glucose + oxygen  → carbon dioxide + water + energy
Human respiratory system
The respiratory system includes:
  • nose
  • nasal cavity
  • pharynx
  • trachea
  • bronchus
  • bronchioles
  • alveoli
  • diaphragm
  • lungs
The flow of air:
  1. Air enters through two external nostrils. The nostrils lead into two nasal passages which are lined with a moist mucous membrane.
  2. The air in your nasal passages enters the pharynx. From the pharynx, air passes into your larynx and then into your trachea.
The lower end of the trachea divides into two tubes/bronchi. Each bronchus (plural: bronchi) connects to one lung.Each bronchus divides continually and ends in bronchioles. Each bronchiole ends in a cluster of air sacs or alveoli (singular: alveolus).Thousands of alveoli are found in lungs, and these alveoli provide a very large surface area for gaseous exchange.Gaseous exchange is possible because alveoli are well‐supplied with blood capillaries.
Breathing is a physical process by which respiratory gases are exchanged with the surroundings.
It is also the movement that brings air into and out of the body.

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