Lower 6 Biology

7/28/2019 Lower 6 Biology

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Lower 6 Biology

1. The cell theorya. All living things are made of one or more cellsb. Cells are the basic units of lifec. Cells come from pre-existing cells

2. The modern version of the cell theory includes the ideas that:-a. Energy flow occurs within cellsb. Heredity information (DNA) is passed on from cell to cellc. All cells have the basic chemical composition (All cells contain DNA)

Prokaryotic cells

1. Cytoplasm contains all the enzymes needed for all metabolic reactions, since there are noorganelles

i.

2. Ribosomes. The smaller (70S) type.3. Nuclear area (nucleoid) containing DNA / Nuclear body. The region of the cytoplasm that

contains DNA. It is not surrounded by a nuclear membrane.

4. DNA. Always circular and not associated with any proteins to form chromatinii.5. Plasmid. Small loops of DNA, used to exchange DNA between bacterial cells.6. Cell membrane/ Plasma membrane. Made of Phospholipids and lipids, like eukaryotic

membranes.

7. Cell wall. Made of murein (not cellulose).8. Capsule. A thick polysaccharide layer outside the cell wall. Used for sticking cells together, as a

food reserve, as protection against desiccation and chemicals.

9. Flagellum (Flagella). A rigid rotating helical-shaped tail used for propulsion. The motor isembedded in the cell membrane. They always rotate clockwise.


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Eukaryotic cells

Both animal cell and plant cell are eukaryotic cells.

1. Cell membrane (Plasma Membrane).a. A thin, flexible layer round the outside of all cells made of phospholipids and lipids.b. It separates the contents of the cell from the outside environment, and controls the

entry and exit of materials.

2. Cytoplasm (Cytosol).a. Solution within the cell membrane.b. It contains the enzymes for glycolysis (the first stage of respiration) and other metabolic

reactions together with sugars, salts, amino acids, nucleotides and everything else

needed for the cell to function. This is where the 1st stage of respiration takes place.

3. Nucleus.a. The largest organelle.b. Surrounded by nuclear envelope, which is a double membrane with nuclear pores-large

holes containing proteins that control the exit of substances such as mRNA and

ribosomes from the nucleus.

c. The interior is called nucleoplasm, which is full of chromatin (DNA/ protein complexcontaining the genes)

d. The nucleolus is a dark region of the nucleus, involved in making ribosomes andprocessing m-RNA.

4. Ribosomes (80S)a. The smallest and most numerous of the cell organelles.b. The sites of protein synthesis.c. Composed of protein and RNA and are manufactured in the nucleolus of the nucleus.

5. Golgi Body (or Apparatus)a. Another series of flattened membrane vesicles.b. Its job is to transport proteins from the RER to the cell membrane for export.


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6. Vacuolesa. Membrane-bound sacs containing a dilute solution.b. Plant cells have large vacuoles that fill most of the cell (90% of the cell, the biggest

organelle in plant cell, can be bigger than nucleus)

c. Function:-i. For excretion of waste (animal cell)

ii. Storage sacs (plants make their own food and need a storage space)iii. Intracellular digestioniv. Space filling (Plant cell)v. Contains water, sugar, starch, pigments-traps light energy for photosynthesis

7. Microvillia. Small finger like extensions of the cell membrane found in some animal cells (gut and

kidney)

b. They increase the surface area of absorptionc. Only visible under the light microscope as the brush border.

8. Cell walla. Animal cell do not have a cell wall.b. Used to give a cell strength and rigidityc. Plant cell walls are made mainly of cellulose

9. Cytoskeletona. A network of protein fibresb. Used for support, transport and motilityiiic. It is attached to the cell membrane and give the cell its shape, as well as holding all the

organelles in position

Compare the structure of prokaryotic and eukaryotic cells


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i

Organelles mean little organs. Basically this means that organelles have specific roles to play roles to play in how

cells work just like organs help the body to function properly as a whole.ii

Chromatin. Mass of genetic materials composed of DNA and proteins that condense to form chromosomes during

Eukaryotic cell division. Chromatin is located in the nucleus of a cell.iii

Motility- the ability to move spontaneously. E.g. stomach contraction that move the food content along from the

stomach to the intestines.

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Lower 6 Biology