2.2. Levels of organisation

Multicellular plants and animals contain many different types of cells. Each type of cell is designed for a particular function.


Levels of organisation: cell --> tissue --> organ --> organ system --> organism

1. Ciliated cells - in the respiratory tract

• Feature: cilia (tiny hairs) that can move mucus
• Function: waft mucus with bacteria and dust away from lungs through the bronchi and trachea

2. Root hair cells 

• Feature: hair gives a large surface area
• Function: absorb water and minerals; anchor the plant firmly in the soil

3. Xylem vessels

• Feature:
• long, thin cells arranged end-to-end to form vessels (tubes)
• cells lack end walls and cell contents (cytoplasm, nucleus)
• walls become lignified
• Function:
• transport water and mineral ions from roots to leaves
• lignin provides strength for stem, makes vessels waterproof

4. Palisade mesophyll cells

 

• Feature: column-shaped cells, packed with chloroplasts
• Function: trap sunlight to make food for the plant by photosynthesis

5. Nerve cells 

• Feature:
• very long and able to conduct electrical impulses
• some have fatty sheath for insulation
• Function: carry electrical impulses to/from the brain and spinal cord

6. Red blood cells

• Feature:
• no nucleus
• contains haemoglobin
• Function: transport oxygen around the body

    

7. Sperm and egg cells

Sperm cells:

• Features:
• tail to swim
• nucleus carries genetic information
• Function: reproduction, by penetrating an egg cell

Egg cells:

• Features:
• large amount of cytoplasm containing yolk droplets, made from protein and fat
• nucleus carries genetic information
• Function: reproduction

Levels of organisation

• Tissue
• a group of cells with similar structures
• cells work together to perform a shared function
• Organ:
• a structure made up of a group of tissues
• tissues work together to perform specific functions
• Organ system:
• a group of organs with related functions
• organs work together to perform body functions

For the original post, click on Cell Functions and Tissues, Organs and Organ systems

For past papers, click here.