Biology

Prokaryotic- Simpler. Smaller (0.5-3.0µm) No nucleus. Cell walls made of a polysaccharide. Few organelles. Small ribosomes. Bacteria and Blue-Green Algae, E.g: E.coli Bacterium.

Eukaryotic - Complex. Larger (20-40µm). Nucleus present. Cellulose wall (plants and algae) Chitin wall (fungi). Many organelles. Large ribosomes. Animal and Plant cells, E.g: Human Liver cell.

Most Eykaryotic cells are adapted to do a particular job.

1) Alveolar epithelium cells line the alveoli in the lungs:allow gases to pass through them easily. Thin, with not much cytoplasm.

2) Epithelium cells in the small intestine:absorb food efficiently. Walls of small intestine have villi (these have microvilli on the surface) to greatly increase the surface area.

3) Palisade mesophyll cells (in leaves) do most of the photosynthesis:contain many chloroplasts to absorb as much sunlight as possible.

Single-celled organisms perform all life functions in their one cell.

Multi-cellular organisms have different cells doing different jobs. Cells are organised into different groups. Similar cells are grouped together into tissues.

SQUAMOUS EPITHELIUM:Single layer of flat cells lining a surface. Pretty common on the body.Cells lining the alveoli are squamous epithelium cells.

CILIATD EPITHELIUM:Has moving hair-like structures called cilia on it. Found on surfaces where things need to be moved, E.g. Cilia wafts mucus along the trachea.

EPITHELIUM:A TISSUE THAT FORMS A COVERING OR LINING

NO EPITHELIUM IN PLANTS - INSTEAD THERE'S EPIDERMIS

Xyloem...is a plant tissue with 2 jobs.

• Transports water around the plant
• Supports the plant

Cells are mostly dead and hollow and are like tubes. They have thick walls for strength.

Phloem...carries sugar around the plant.

• Each cells has end walls with holes in them so sap can move easily through them
• The end walls are called sieve plates.

A leaf is a plant organ, made up of the following tissues.

• Lower epidermis-contains stomata (holes) to let carbon dioxide in and out.
• Spongy mesophyll-full of spaces to let gases circulate.
• Palisade mesophyll-most photosynthesi takes place here.
• Xylem-carries water to the leaf.
• Phloem-carries sugars away from the leaf.
• Upper epidermis-covered in a waterproof waxy cuticle to reduce water loss.

The liver is an animal organ.

• Liver cells are the main tissue
• Blood vessels provide oxygen and food for the liver cells.
• Connective tissue holds the organ together

Blood vessels aren't a tissue though. They contain several tissues (epithelium, muscle etc) so they're actually organs.