TOPIC ECOSYSTEM

Part 1: Characteristics of Living Organisms

Any living organism can be classified based on seven characteristics.

Such characteristics are required to ensure the survival of a species within a

community in an ecosystem.

Organisms must be allowed to pass down the genes to their offspring.

These characteristics can be remembered using the mnemonic MRSGREN.

M.R.S.G.R.E.N stands for:

A Movement

Organisms need to move to find shelter, food, and partners for

reproduction to ensure the survival of a species.

Responding to the stimuli allows organisms to avoid danger such as

being hunted by predators.

B 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 2: 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 3: The word equation (above) and chemical equation (below) for anaerobic respiration in animal cells.

Figure 1: A cheetah chasing after its

prey.

» Plant cells:

Figure 4: The word equation (above) and chemical equation (below) for anaerobic respiration in plant cells.

C Stimuli

Organisms need to respond to the stimuli or external

environment in their surroundings. This allows them to

avoid danger or find shelter.

In the environment, such stimuli can be divided into:

a) biotic factors

» living organisms within an ecosystem and how the

organisms interact with each other

» Eg: human activities, competitors, prey-predator,

parasitism, commensalism, mutalism

b) abiotic factors

» non-living physical and chemical factors that make up

the ecosystem in which a community of different organisms and species live in

» Eg: light, water availability, oxygen availability, soil pH

D Growth

All organisms will undergo a certain growth phase in

their life cycles. The growth implies an accumulation of

organic matter and expenditure of energy. Hence, they

require nutrients for the cells to grow.

Remember, cells will experience growth in the form of

mitosis. Mitosis is a type of nuclear division that allows

the cells to be replicate similar copies. You can relate the

mitosis process to the ecosystem.

E Reproduction

There are two types:

a) asexual

» Organisms that undergo asexual reproduction produce

similar daughter cell copies. The copies will be diploid

cells, 2n.

» Effective cloning.

» Mitosis is the process involved. The concepts here are a

repetition and linked.

» Requires energy and nutrition to reproduce properly.

b) sexual

» Organisms that undergo sexual reproduction will produce haploid cells, n i.e. half of the

chromosomes from one parental cell.

» Meiosis is the process involved.

Figure 5: Similar to animals, plants respond to

stimuli under different circumstances.

Figure 6: The exponential and logistic growth graphs

over time for the growth of organisms.

Figure 7: A cell undergoing asexual

reproduction by means of mitosis at the

anaphase stage.

» The haploid cells involved are called gametes. Such cells

will produce a significant and variant genetic makeup.

» The male and female gametes will produce unique

individuals by crossing-over and random fertilisation.

» Survival of the fittest – only the more dominant and

stronger genes will be naturally selected to be passed

down to the offspring from the parents.

F Energy

As mentioned in the respiration section, more energy is

produced by aerobic respiration.

Glucose and ATP are both energy sources. ATP is utilised more

than glucose in cellular activities.

ATP is known as the universal

energy. There are three

reasons why ATP is utilised

than just glucose.

(1) Easily/rapidly hydrolysed

» energy is provided instantly

(2) Releases a small amount of energy

» reduces wastage of energy

(3) Utilises one enzyme

» uses one enzyme as compared to glucose which utilises many

enzymes for aerobic respiration

The mitochondria organelle produces ATP energy from the aerobic respiration of glucose.

Glucose is synthesised by plant cells in the chloroplast.

After consumption of producers by the consumers, glucose will only then be taken up into the system.

G Nutrition

The elements are H, C, O, N, S and P are the important

building block elements for many macromolecules

such as carbohydrates, proteins, lipids and nucleic

acids (DNA).

All living organisms require essential nutrients to:

» Generate energy via cell respiration

» Build new cells

» To allow cell repair

» To allow cells to excrete and communicate

» To build new molecules as required by a cell

» To maintain a balanced internal environment

Figure 8: Random fertilisation in sexual

reproducing organisms creates unique

characteristics.

Figure 9: Crossing-over at the first

stage of meiosis contributes towards

producing unique individuals and

gives rise to diversity.

Figure 10: The structure of adenosine

triphosphate (ATP).

Figure 11: The basic organic building blocks required

in cells for their cellular activities purposes.