TOPIC ECOSYSTEM

Part 2: Respiration & Photosynthesis

Respiration and photosynthesis are two important processes in the ecosystem.

A balance of oxygen and carbon dioxide is important to maintain the well-being of

the ecosystem.

This chapter is crucial because we will see these two concepts in many other sub-

topics.

Respiration

Respiration is a chemical process of breaking down sugar (in the form of glucose) to generate energy

for cellular activities and metabolic activities.

There are two types of respiration:

(a) Aerobic respiration

» Occurs in the presence of oxygen.

» The glucose is broken down into carbon dioxide, water and releases energy.

» Such energy is in the form an energy carrier molecule i.e. ATP (adenosine triphosphate).

» The energy released is utilised for many cellular activities like DNA replication, transcription and

translation.

» Occurs in both animals and plants.

Figure 1: The chemical equation (above) and word equation (below) for aerobic respiration.

(b) Anaerobic respiration

» Occurs in the absence of oxygen due to the stress of the environment on the cells.

» Animal and plant cells can be stressed due to the lack of oxygen and produce different

products.

» The energy produced by this reaction is less as compared to the aerobic respiration.

» Animal cells:

Figure 2: The word equation (above) and chemical equation (below) for anaerobic respiration in animal cells.

» Plant cells:

Figure 3: The word equation (above) and chemical equation (below) for anaerobic respiration in plant cells.

Photosynthesis

Photosynthesis is the opposite process of respiration; it

is the process of building up sugar (in the form of

glucose, C6H12O6) in the presence of sun light.

The glucose generated will be stored in the form of

starch.

This occurs only in plant cells.

Why?

» Plant cells contain chloroplast, an organelle,

which contains a green pigment called chlorophyll.

» Chlorophyll is a green pigment found in chloroplast which functions to absorb the energy from the

sun and converts into chemical energy i.e. glucose.

» Not all the energy from the sun will be absorbed.

Photosynthesis occurs only during the day time. In the process, it releases oxygen into the

environment.

Plants are responsible to regulate the amount of oxygen and carbon dioxide in the atmosphere.

Figure 4: Word equation for photosynthesis.

Figure 5: Symbol or chemical equation for photosynthesis.

Do plants even undergo respiration?

» You might be surprised but yes, they do!

» Plants undergo both photosynthesis and respiration. During the day, they will collect enough light

energy to create and store enough glucose (as starch) to last them at night.

» At night, sunlight is not available and therefore no photosynthesis could occur. However, with the

starch collected during the day, it will be converted into glucose and from there respiration will

occur.

Compare and contrast between respiration & photosynthesis

» There are many other similarities and differences between the two processes. Try to think of some

on your own.

Respiration Photosynthesis

Breakdown of glucose Process Buildup of glucose

Glucose, oxygen Substances Carbon dioxide, water, energy,

chlorophyll

Carbon dioxide, water, energy Products Glucose, oxygen

Mitochondria Organelles involved Chloroplast

Figure 3: The green substances in the plant cells are

chloroplasts which contain chlorophyll.