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Sunday, April 18, 2010

Structure of Plant cell and it's organelles functions.

Figure 1.Plant Cell

Organelles' functions:-

1.Nucleus:-
i)Within nucleus, the chromosomes are in a loosely coiled state known as chromatin (except during nuclear division).
ii)Chromosomes contain DNA which is organised into functional units called genes.
iii)Genes control the activities of the cell and inheritance.
iv)Division of the nucleus precedes cell division.
v)Within nucleus, the nucleolus manufactures ribosomes, using the information in its own DNA.



2.Ribosomes:-
i)The space inside the sac forms a compartment separate from the surrounding cytoplasm.
ii)It goes on to the Golgi apparatus.
iii)Ribosomes are the sites of protein synthesis.
iv)At high magnifications, the ribosomes are seen having two parts, a smaller and a larger subunit.
v)They are found free in the cytoplasm as well as on the rough ER.
vi)They are very small organelles and made of RNA and protein.
3. Endoplasmic Reticulum(ER):-
i)Separate into two groups-[Rough Endoplasmic Reticulum and Smooth Endoplasmic Reticulum].
ii)In some area, the ER lacks ribosomes and appears smooth.
iii)This called smooth ER and the ribosomes-covered ER is called rough ER.
iv)The membranes form a system of flattened sacs, called cisternae.
v)The smooth ER synthesis lipids and steroids-cholesterol and reproductive hormones.
vii)The protein manufactured on the ribosomes are transported throughout the cell by the rough ER.
4.Golgi Apparatus:-
i)The apparatus collects, processes and sorts molecules (particularly protein from the rough ER).
ii)Ready to be transported in Golgi vesicles either to other parts of the cell or out of the cell(secretion).
iii)Golgi Apparatus are also used to make lysosomes.
5.Mitochondria:-
i)Slightly larger than lysosomes and are surrounded
by two membranes-an envelope.
ii)The inner part is folded to form finger-like cristae which project into the interior solution or matrix.
iii)Main function is to carry out the later stages of aerobic respiration.
iv)As a result of respiration, they make ATP, the universal energy carrier in cells.
v)They are also involved in synthesis of lipids.
6.Plasma Membrane:-
i)This consists of two dark lines(heavily stained) either side of a narrow, pale interior.
ii)Partially permeable, controlling exchange between cell and its environment.
7.Cell wall:-
i)Give mechanical support to herbaceous plants with weak stems.
ii)Allow water and mineral salts to move through and along it, as it is permeable and rigid.
iii)Prevent the movement of certain substances.
iv)Direct the pattern of growth and shape of a cell by the cellulose fibril arrangement in the cell wall.
v)Store food reserves, such as hemicelluloses.
8.Chloroplast:-
i)Contain enzymes necessary for the photosynthesis light-independent reactions in the stroma.
ii)Contain chlorophyll and other pigments that are required for the photosynthesis light-dependent reactions in thylakoids.
iii)Store the photosynthetic products in the form of starch grains.
9.Vacuole:-
i)Provide support for plants by enabling water molecules to pass through via osmosis and maintain turgidity.
ii)Contain hydrolytic enzymes and play a similar role as lysosomes.
iii)Contain pigments to provide colour for parts of the plant, especially the flowers.
iv)Temporarily store waste products such as tannin and alkaloids.
v)Temporarily store food such as sucrose.

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