1. Endoplasmic reticulum
(EM) (x94000 app.)

3. 4.2.6 Endoplasmic reticulum
- an elaborate system of membranes forming a cytoplasmic skeleton
- an extension of the out nuclear membrane
Cisternae: flattened sacs formed by the membranes
Rough endoplasmic reticulum: membranes are lined with ribosomes
Rough ER is concerned with protein synthesis and is abundant with cells which are rapidly growing or secreting enzymes
Smooth endoplasmic reticulum: membranes lack ribosomes

5. Functions of the ER:
1 Provides a large surface area for chemical reactions
2 Provides a pathway for the transport of materials through the cell
3 Produces proteins, especially enzymes
4 produces lipids and steroids
5 Collects and storing synthesized materials
6 Provides a structural skeleton to maintain cellular shape (e.g. smooth ER of a rod cell of retina)

6. Golgi apparatus of an olfactory bulb cell
Golgi apparatus (EM) (x30000 app.)

7. 4.2.7 Golgi apparatus (dictyosome)
- similar to smooth ER but is more compact
vesicles: small membranous sacs pinching off from the cisterna
- normally only one Golgi apparatus in animal cells but a large number of stacks known as dictyosomes in plant cells
- well developed in secretory cells and neurones for secretory functions

10. Functions:
1 adding carbohydrates to proteins to form glycoprotiens
2 produce secretory enzymes, e.g. pancreatic enzymes
3 produce new cell walls by secreting carbohydrates
4 transport and store lipids
5 form lysosomes

11. 4.2.8 Lysosomes
- bounded by a single membrane which contains enzymes (mostly hydrolases)
- abundant in secretary cells & in phagocytic white blood cells

12. 1 Digest material which the cell consumes from the outside by phogocytosis, e.g. white blood cells digest bacteria, amoeba digests food
2 Digest part of a cell or worn-out organelles, autolysis for dead cells
3 Release enzymes outside the cell (exocytosis) to break down other cells, e.g. reabsorption of tail of tadpoles during metamorphosis
Therefore, they are abundant in secretory cells and phagocytic cells.

13. - small spherical membrane-bounded bodies; slightly granular structure
4.2.9 Microbodies
- small spherical membrane-bounded bodies; slightly granular structure
- contains enzymes (mostly catalase) to break down H2O2:
2 H2O  2 H2O O2
- H2O2 is a potentially toxic by-product of many biochemical reactions in cell, particularly active cells like the liver cells A B C D E
nucleus
A: heterochromatin
B: euchrromatin
C: nucleolus
D: nuclear pores
E: microbody

14. Vacuoles
- tonoplast: single membrane around the vacuole
- containing a solution of mineral salts, sugars, amino acids, wastes and sometimes anthocyanins
- large and central in plants ;
numerous but small in animal cells, e.g. food vacuole, phagocytic vacuole and contractile vacuole

15. Functions:
1 temporary food reservoir of sugars & amino acids
2 anthocyanins (coloured pigments) attract pollinating insects, animals for fruit dispersal
3 temporary stores for wastes, e.g. tannins, and to be removed through leaf cells when leaves fall
4 occasionally contain hydrolytic enzymes to act as lysosomes
5 provide turgidity to herbaceous plants & seedlings

16. Non-membranous Structures
Ribosomes
- small cytoplasmic granules of RNA molecules for protein synthesis
- around 20 um in diameter in eukaryotic cells (80S)
but slightly smaller in prokaryotic cells (70S)
- account for 20% of the mass of a cell
polysomes: ribosomes occur in groups assciated with rough ER or occur freely within cytoplasm

18. Storage granules
- soluble form as sugars in vacuoles of plant cells
- insoluble forms:
starch grains - in chloroplasts & cytoplasm;
in specialized leucoplast (amyloplast)
glycogen granules – in animals cells
lipid droplets – both plant and animal cells
Leucoplast are colourless plastids (double membraned organelles in plants)