IB Biology Topic A2.2.7 Processes of Life in Unicellular Organisms Revision Notes (SL/HL)

IB Biology Topic A2.2.7 Processes of Life in Unicellular Organisms Revision Notes (SL/HL) | RevisionDojo

Written by official IB examiners

A Single Cell Performs Every Function of Life

A unicellular organism carries out all the functions of life inside one cell.
These functions are homeostasis, metabolism, nutrition, movement, excretion, growth, response to stimuli, and reproduction.
Two organisms show how this works: Paramecium, a freshwater heterotroph, and Chlamydomonas, a photosynthetic autotroph.

Tip

"Hot Moms Need Many Exciting Games, Really Relaxing" is an easy way to recall the eight functions of life.
- H: Homeostasis, keeping the internal environment stable.
- M: Metabolism, the chemical reactions that sustain life.
- N: Nutrition, obtaining energy and nutrients.
- M: Movement, changing position in the environment.
- E: Excretion, removing metabolic waste.
- G: Growth, increasing in size and mass.
- R: Response to stimuli, reacting to changes in the surroundings.
- R: Reproduction, producing offspring to continue the species.

Paramecium and Chlamydomonas Are the Key Examples

1. Homeostasis Keeps the Internal Environment Stable

A cell must hold its internal conditions steady even as the outside environment changes.
This includes regulating water content, pH, ion concentration, and temperature.

Example

Paramecium lives in freshwater, so water constantly enters the cell by osmosis.
Its contractile vacuoles pump this excess water out to stop the cell swelling and bursting.

2. Metabolism Powers Every Cellular Activity

Definition

Metabolism

The sum of all chemical reactions occurring in an organism to maintain life, including reactions that break down molecules for energy (catabolism) and reactions that build molecules for growth and repair (anabolism).

Metabolism is the full set of enzyme-controlled reactions that release and use energy in the cell.
In a unicellular organism these reactions take place in the cytoplasm and organelles.

Example

Chlamydomonas uses its chloroplast to capture sunlight and make glucose.
That glucose is broken down in respiration to release energy for jobs like protein synthesis and cell division.

3. Nutrition Supplies Energy and Raw Materials

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Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

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A Single Cell Performs Every Function of Life

A unicellular organism carries out all the functions of life inside one cell.
These functions are homeostasis, metabolism, nutrition, movement, excretion, growth, response to stimuli, and reproduction.
Two organisms show how this works: Paramecium, a freshwater heterotroph, and Chlamydomonas, a photosynthetic autotroph.

Tip

"Hot Moms Need Many Exciting Games, Really Relaxing" is an easy way to recall the eight functions of life.
- H: Homeostasis, keeping the internal environment stable.
- M: Metabolism, the chemical reactions that sustain life.
- N: Nutrition, obtaining energy and nutrients.
- M: Movement, changing position in the environment.
- E: Excretion, removing metabolic waste.
- G: Growth, increasing in size and mass.
- R: Response to stimuli, reacting to changes in the surroundings.
- R: Reproduction, producing offspring to continue the species.

Paramecium and Chlamydomonas Are the Key Examples

1. Homeostasis Keeps the Internal Environment Stable

A cell must hold its internal conditions steady even as the outside environment changes.
This includes regulating water content, pH, ion concentration, and temperature.

Example

Paramecium lives in freshwater, so water constantly enters the cell by osmosis.
Its contractile vacuoles pump this excess water out to stop the cell swelling and bursting.

2. Metabolism Powers Every Cellular Activity

Definition

Metabolism

Metabolism is the full set of enzyme-controlled reactions that release and use energy in the cell.
In a unicellular organism these reactions take place in the cytoplasm and organelles.

Example

Chlamydomonas uses its chloroplast to capture sunlight and make glucose.
That glucose is broken down in respiration to release energy for jobs like protein synthesis and cell division.

3. Nutrition Supplies Energy and Raw Materials

Definition

Paywall

(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Note

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

Excepteur sint occaecat cupidatat non proident

Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

IB Biology Topic A2.2.7: Processes of Life in Unicellular Organisms Notes

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

A Single Cell Performs Every Function of Life

Paramecium and Chlamydomonas Are the Key Examples

1. Homeostasis Keeps the Internal Environment Stable

2. Metabolism Powers Every Cellular Activity

3. Nutrition Supplies Energy and Raw Materials

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

A Single Cell Performs Every Function of Life

Paramecium and Chlamydomonas Are the Key Examples

1. Homeostasis Keeps the Internal Environment Stable

2. Metabolism Powers Every Cellular Activity

3. Nutrition Supplies Energy and Raw Materials

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account