Biology Unit 2 Notes

2.3.1

Organelle Structure and function

nucleus
 enclosed in double membrane with pores
 contains chromosomes with genes made of DNA to control protein synthesis

ribosomes
 made of RNA and protein
 free in cytoplasm or attached to RER
 site of protein synthesis

rough endoplasmic reticulum
 interconnected sacs with ribosomes attached
 transport proteins to other parts of cell

smooth endoplasmic reticulum  synthesis of lipids and steroids

mitochondria
 double membrane – inner folded into cristae
 site of later stages of aerobic respiration

centrioles
 one pair found in animal cells
 made of protein microtubules
 involved in spindle formation and cellular transport

lysosomes
 digestive enzymes wrapped in membrane
 breakdown of unwanted structures or old cells

nucleolus
 dense body in nucleus
 synthesis of ribosomes

2.3.2

Proteins synthesised on the ribosomes of the RER are moved to other parts of the cell through the cavities of the endoplasmic reticulum.

The Golgi apparatus is a stack of membrane-bound sacs formed from fused vesicles from the ER.

Proteins are modified here and packaged in vesicles. Some eg enzymes and hormones are released from the cell.

See Figure 3.9 on page 101.

2.3.3

The cells described above, with membrane-bound organelles are eukaryotic.

Organisms with eukaryotic cells are classified into 4 kingdoms: Animals, Plants, Fungi and Protoctists.

The 5th kingdom is the Prokaryotes, with prokaryotic cells which:
 are smaller than eukaryotic cells
 have no membrane-bound organelles
 have no nucleus
 have circular DNA, not associated with protein
 have small rings of DNA, called plasmids
 always have a cell wall

To compare prokaryotic & eukaryotic cells, see Figures 3.4 and 3.8 on pages 98 & 100.

2.3.4
Mitosis is a type of cell division, which retains the full or diploid number (2n) of chromosomes.

In