Section 2: Structures and functions in living organisms

a) Levels of organisation
b) Cell structure
c) Biological molecules
d) Movement of substances into and out of cells
e) Nutrition
f) Respiration
g) Gas exchange
h) Transport
i) Excretion
j) Coordination and response

a) Levels of Organisation

2.1 describe the levels of organisation within organisms: organelles, cells, tissues, organs and systems

b) Cell Structure

2.2 recognise cell structures, including the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and vacuole

2.3 describe the functions of the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and vacuole

2.4 describe the differences between plant and animal cells

 image001

Animal cell

  1. A cell membrane is like a sieve, it controls what goes in and out of the cell. 
  2. The cytoplasm is where the chemical reactions take place, the mitochondria in the cytoplasm is where respiration takes place to release energy. The cytoplasm also contains enzymes that control the chemical reactions. 
  3. The nucleus is like the 'brain' of the cell, it controls the cell, telling it what to do. It also contains DNA which is important when the cell reproduces. 

 image002

Plant cell

Plant cells have extra features:

  1. They have a cell wall, this is made of cellulose. It gives the cell shape and structure and provides support. It also means the cell can't burst, it becomes turgid when it is full of water. (The cell walls are actually impermeable to water, which is why they have small gaps in them called plasmodesmata which allow water to enter via osmosis...)
  2. They have chloroplasts which contain chlorophyll-the green pigment that allows it to absorb light energy and convert it to chemical energy during photosynthesis. Plants are autotrophs-they can make their own food. 
  3. Plant cells have a permanent vacuole that contains cell sap, it provides support. It is also basically a storage and removes waste, and provides/maintains the cell structure. 

Feature

Animal Cell

Plant Cell

Nucleus

Yes

Yes

Cytoplasm

Yes

Yes

Cell Membrane

Yes

Yes

Mitochondria

Yes

Yes

Vacuole

No

Yes

Cell Wall

No

Yes

Chloroplasts

No

Yes