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Plasma Membrane
- The plasma membrane is a thin, permeable membrane which surrounds the cell. It controls any exchange in or out of the cell.
- The fluid mosaic model was suggested by S. J. Singer and G. L. Nicolson in 1972. They believed that the plasma membrane around cells was made up from a phospholipid bilayer. This bilayer, they said, was made up from two layers of lipids, each with their hydrophobic tails facing inwards and their hydrophilic heads forming the surface.
- As well as lipids, the plasma membrane is made up of glycolipids, glycoproteins, transmembrane proteins and surface proteins.
- The plasma membrane acts as a barrier against undesirable substances and cells but has many other uses too. The plasma membrane contains glycolipids and glycoproteins which allow it to be identified by other cells.
Inside an Animal Cell
Nucleus
- The largest organelle within the cell.
- It is enclosed by two membranes in an envelope.
- The nucleus contains chromatin, which is the extended form taken by chromosomes during interphase, as well as a nucleolus.
- Acts as the control centre of the cell.
Endoplasmic Reticulum (ER)
- A system of flattened membranes called cisternae (mainpoint: I spelt it wrong in the diagram, sorry).
- It’s a continuous single membrane which is also the nuclear outer-membrane.
- When ribosomes are found on its surface it’s known as a rough ER and it transports any proteins made by the ribosomes.
Mitochondria
- Site of the Krebs Cycle & Electron Transport Chain in Respiration.
- Surrounded by two membranes, the inner folded forming cristae.
- Contains ribosomes, a circular DNA molecule and a matrix.
- A cell can contain anywhere between 1 to a thousand mitochondria.
Ribosomes
- Very small organelles consisting of a larger and a smaller subunit.
- Site of protein synthesis.
- Ribosomes are responsible for making proteins from genetic information given to it by mRNA and taken from the nucleus.
Golgi Body/Apparatus
- Similar in structure to the endoplasmic reticulum (ER) but is more compact and is made up of flattened sacks.
- It’s functions include transporting and storing lipids, producing glycoprotein, forming lysosomes and producing secretary enzyme.
Lysosome
- This contains digestive enzymes from the remainder of the cell and one of its purposes is destroyed old organelles.
Plant Cell
Chloroplasts
- Chloroplasts are large organelles, usually in a biconvex shape, and about 4-10μm long and 2-3μm wide.
- Within plants most chloroplasts are found in the mesophyll cells of leaves.
- The stages of photosynthesis take place within the chloroplast, stage 1 within the granum and stage 2 within the stroma.
Differences between Animal and Plant Cells
| Structure | Animal Cell | Plant Cell |
|---|---|---|
  |   | |
| Plasma Membrane | ||
| Cell Wall |  | |
| Nucleus |  |  |
| Endoplasmic Reticulum |  |  |
| Mitochondria |  |  |
| Ribosomes |  |  |
| Golgi Body/Apparatus |  |  |
| Chloroplasts |  |
Frequently Asked Questions
What is a plasma membrane?
The plasma membrane is the outermost boundary of an animal cell (in plants surrounded by cell walls) that allows the selective transport of substances across it. It comprises a lipid bilayer in which protein molecules are embedded.
What are the different organelles found in animal cells?
Several organelles are found in animal cells, such as the nucleus, mitochondria, ribosomes, lysosomes, Golgi apparatus, and endoplasmic reticulum.
What are chloroplasts?
Chloroplasts are large biconvex organelles found in the mesophyll cells of plants. They contain photosynthetic pigments (chlorophylls and carotenoids) to absorb sunlight and carry out photosynthesis.
What is the outermost covering in plant and animal cells?
The outermost covering in the plant cell is the cell wall, while in the animal cell, the outermost covering is the cell membrane (plasma membrane).