The Ultrastructure of Cells

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Unit 1.2 ­ Ultrastructure of Cells
The ultrastructure of a cell can only be seen through an electron microscope.
Eukaryotic cells have internal cell membranes. Many organelles are membrane bound. This
is to divide the labour; each membrane bound organelle has a function. This is called
Membranes are essential inside the cell for:
Separating areas from the rest of the cytoplasm e.g. lysosomes
Many metabolic processes involve enzymes. Membranes give a large surface area
for these to attach e.g. mitochondria
ATP is synthesized using membranes in the mitochondria
Providing transport systems within the cell e.g. endoplasmic reticulum
Animal Cell - Pink
Plant Cell ­ Green
Both ­ Blue
Plasma Membrane
1. Keeps the contents of the cell together
2. Controls what moves into and out of the cell
3. Partially permeable
1. Largest of the organelles
2. Controls cell activity
3. Retains the chromosomes
4. Two membranes called the cell membrane surround it
5. Nuclear pores allow the exchange between cytoplasm and chromatin
6. Material inside is called nucleoplasm and contains chromatin, made up of loosely
coiled DNA attached to proteins
7. During cell division chromatin condenses, forming chromosomes
8. Nucleolus makes ribosomal RNA and assembles ribosomes
1. Two lie at right angles outside the nucleus in a region known as the centrosome
2. Hollow tubes made up of microtubules
3. They migrate to opposite poles at cell division where the microtubules make the
spindles for cell division
Endoplasmic reticulum (ER) and ribosomes
1. Membranes of this structure form flattened sacs called cisternae
2. Rough ER- Ribosomes are attached. They transport proteins made by ribosomes
made around the cell
3. Smooth ER- No ribosomes attached. Make steroids and lipids

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1. Have a small & large sub unit made up of RNA and protein.
2. Important in protein synthesis
3. Can be free in cytoplasm or attached to the RER.
Golgi Body
1. Stack of flattened sacs
2. Vesicles bud off the SER and break down to form Golgi vesicles
3. Collects, processes and sorts molecules ready for transport to Golgi vesicles to other
parts of/out the cell
4. Make lysosomes, secretory enzymes and glycoproteins
5.…read more

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Cell Wall
1. Made of cellulose
2. Gives strength and support
3. Allows water in and out as a fixed shape
1. Tiny pores between neighbouring cells
2. Link cells
3. Contain ER enabling movement of material between cells
1. Surrounded by a membrane called the tonoplast
2. Contains cell sap
3. Regulates the cells water intake and removal
1. Enclosed by a double membrane
2. Stroma is a colourless matrix containing ribosomes, lipids, circular DNA and starch
3.…read more


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