Stage 1 SACE - Cell Theory

• Living things are distinguishable from non-living things

• The cell theory unifies all living things

• Living things are made up of one or more cells

Cells:

• Are the structural and functional units of life

• Come from pre-existing cells

• Contain hereditary material

• The cell is the smallest independent unit of life

Cell theory

A cell is the smallest independent unit of life.

Cell theory unifies all living things, and is made up of 3 key ideas:

1. Cells are the smallest structural and functional units of life

2. All cells come from pre-existing cells (through cell division)

3. Cells contain hereditary (genetic material)

Life

Life is a characteristic of a living thing without a clear definition.

Currently, something to be considered ‘alive’ it must meet the following 7 characteristics:

• Movement

• Reproduction

• Stimulus (eg. pain, light, sound)

• Grow

• Respiration (oxygen)

• Excrete waste

• Nutrition (eating other organisms or photosynthesis)

• MRSGREN

• Homeostasis (the ability of the body to maintain a stable internal environment despite changes in external conditions)

Unicellular organisms

They are made up of only one cell. Engulf their food (usually smaller organisms such as bacteria). All 7 of the key life processes occur within this one. 

• Eg. Paramecium and amoeba

Amoeba

Feeding

• Eats tiny plants/bacteria

• Temporary ‘arms’ surround food and bring it into the cell vacuole

Movement

• Called ’cytoplasmic streaming’ 

• Cytoplasm moves in one direction and the rest of the cell follows

Reproduction

• One parent divides into two (binary fusion)

Removal of Waste

• Waste removed by vacuoles 

Paramecium

Feeding

• Eats tiny plants/bacteria

• Has a structure called a ‘gullet’

• Tiny hairs sweep food into this gullet

Movement

• Swims using tiny hairlike structures called cilia

Reproduction

• Divides into two by binary fusion (can divide up to 2-3 times a day)

Removal of Waste

• Waste removed by valucoles