3. Cell membrane (x 12000)

4. 4.2.2 Cell membranes
Functions:
1 A boundary between the cell and its environment
2 It is selectively permeable
Structure
The protein-phospholipid sandwich (Davson-Danielli model)

5. Structure
The protein-phospholipid sandwich (Davson-Danielli model)
- phospholipid molecules form a bimolecular layer:
hydrophobic tails - attracts water
hydrophilic heads - repels water
- protein layer: on either side of the phospholipid layer

7. The fluid-mosaic model (Singer-Nicholson model)
- phospholipid molecules unchanged but is capable of movement (fluid)
- protein molecules varied in size and have less regular arrangement (mosaic):
some proteins occur on the surface of the phospholipid laer (peripheral);
some extend into the phospholipid layer (integral);
some extend completely across the phospholipid layer (transmembrane)
- proteins appear dotted throughout the phospholipid layer in a mosaic pattern
- proteins have many functions, e.g. support, transport and their specificity enables them to perform many specific functions which vary from cell to cell

8. mosaic
fluid
transmembrane
peripheral
integral

9. 83-II-1

10. 98-I-4

11. Liver cell nucleus (EM)
Nucleus (EM) (x app.)

12. Membranous Organelles
4.2.3 The nucleus
nuclear envelope: double-membraned, with pores to allow large molecules (RNA) to pass through 
nucleoplasm: cytoplasm of the nucleus
chromatin: coils of DNA bound to proteins, invisible (visible as chromosomes)
heterochromatin: denser, more darkly staining areas of chromatin
nucleolus: 1 or 2 round bodies manufacturing ribosomal RNA and assemble ribose It is not an organelle. Why?
Because it is not membrane bounded

13. Functions of a nucleus:
1 To contain the genetic material (chromosomes) of a cell
2 To act as a control centre for activities of a cell
3 DNA carries the instructions for the synthesis of proteins
4 Produces ribosomes and RNA
5 Essential for cell division

14. Chloroplast

17. 4.2.4 The chloroplast (4-10 um long & 30 nm thick)
plastids: double membraned organelles containing chlorophyll & carotenoids and carry out photosynthesis
chloroplast envelope: outer membrane similar to plasma membrane, inner membrane is folded into a series of lamellae
stroma: a colourless, structureless matrix (background fluid)
grana: stacks of coin-like structure containing thylakoids
thylakoid: flattened sacs of granum holding chlorophyll for photosynthesis, intergranal lamellae (large thylakoid) join grana together
starch grains: temporary stores for the products of photosynthesis
DNA & oil droplets: DNA as genetic materials of chloroplast; oil droplets as energy reserve

18. Mitochondria
Mitochondrion x15000

19. Mitochondria (EM) (x 15000 app.)

21. 4.2.5 The mitochondrion (lengths vary from 1 to 10um) Double membrane:
outer controls the entry & exit of chemicals;
inner is folded to form cristae to increase the surface area for respiration to occur.
The surface of the cristae have stalked granules along its length.
Matrix:
contains protein, lipids and traces of DNA & electron dense granules;
functions as sites for stages of respiration;
Highly active cells may possess up to 1000 mitochondria in a single cell, e.g. sperms & muscles

23. 97-II-1(c)