Page 21 - PRE-U STPM BIOLOGY TERM 1

Biology Term 1 STPM Chapter 2 Structure of Cells and Organelles

Exam Tips (vii) They cause membrane invagination and evagination during
endocytosis and exocytosis.
Remember: membrane,
cell wall and cytoplasm (viii) They cause the protrusion of pseudopodium during
are cell components, not amoeboid movement in the white blood cells.
organelles but microtubules
and microfilaments are (ix) They assist in the cleavage process during cytokinesis of
considered as organelles. animal cells after nuclear division.
2 (c) Intermediate filaments
(i) The intermediate filaments are filaments bigger than the
Summary microfilaments but smaller than the microtubules, with
diameter between 8 to 12 nm and are only found in animal
Cellular components of cells.
typical plant and animal cell (ii) The filaments are made up of 4 long strands of α-helix
1. Plasma membrane coiled fibrous proteins, each consisting of only secondary
• Phospholipid
• Cholesterol coiled polypeptide.
• Protein (iii) There are several types of intermediate filaments with each
• Carbohydrate composing of only one type of protein, including one with
2. Cell wall
• Primary – celulose keratin.
• Secondary + lignin (iv) They are very stable and branched, forming a network of
3. Cytoplasm
• Cytosol – water, gases, cytoskeleton in the cytoplasm and nucleus.
ions, carbohydrates, (v) Each type of cell has its own arrangement and types of
amino acids, protein. For example, the cells in the skin epithelium or
nucleotides, vitamins
and proteins forming the nail, hair and horn have keratin filaments,
• Cytoskeleton – which are different from those in the muscle and nerve
microfilament, cells.
microtubule and
intermediate filament (vi) They maintain the shape of the cell including the nucleus.
(vii) They distribute the organelles and support them in the
cytoplasm.
(viii) They help some specialised cells to perform their functions.
Some examples include the nail-producing cells to form
nails, and neurone to transmit impulses.

Structure and Functions of Organelles
Nucleus

1. The nucleus is the largest organelle in the eukaryotic cell and
functions to control all activities of the cell.

2. It is found in all cells, except in the red blood cells of mammals and
the sieve tubes of phloem in flowering plants.

3. The nucleus is normally found in the centre of the cell but in matured
plant cells, it is pushed to one side of the protoplast by the big sap
vacuole.
4. There is one nucleus per cell, however, in some exceptional cases, two
are found in Paramecium and abnormal liver cells.
5. It is normally spherical or oval in shape, but it may be cylindrical or
lobed in the white blood cells. The shape can later be changed.

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