Page 29 - PRE-U STPM BIOLOGY TERM 1

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Biology Term 1 STPM Chapter 2 Structure of Cells and Organelles

2015 Mitochondria
1. Mitochondria are the ‘power houses’ of the cell, where energy in the
form of ATP is formed. The energy comes from cellular respiration
Language Check where ATP is formed from the bonding of phosphate to ADP.
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• Mitochondrian – singular 2. Mitochondria are found in every eukaryotic cell. Their location
Mitochondria – plural inside the cell is not fixed as they can move around.
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3. Protozoa and yeasts have only one mitochondrion per cell. In the
liver cells, there are between 500-1,400 mitochondria per cell whereas
in the root cap cell of maize, they vary between 100-3,000 per cell.
The number can be increased when a cell becomes more active and
needs more energy.
4. Each mitochondrion can divide to form two mitochondria. This
happens when the cells become active or just before cell division.
However, such division cannot occur outside the cells, as it requires
enzymes coded by the nucleus.
5. Usually they are spherical, oval or sausage-shaped. It can be like a
rod or a spiral. The shape is changeable.
6. Mitochondria are considered medium size organelles in the cell.
They can hardly be observed under light microscope. Their diameter
is 0.25-1 µm and length 3.5-10 µm.
7. They have 65-75% protein, 25-35% lipid and about 0.5% of nucleic
acids.
8. They have an envelope with liquid matrix within as shown below.

Outer membrane
Cristae

Inner membrane

Matrix
Stalked granule

Figure 2.18 A mitochondrion
9. Its envelope is made up of two layers of lipoprotein membranes with
an inter-membrane space in between.
10. The outer membrane is smooth with no granule attached. It has a lot
of pores with diameters between 2.5-3.0 nm. Such pores are part of
the channel proteins or translocase for the passage of ADP or ATP
+
and NAD or NADH.
11. The inner membrane is folded to form cristae that are tube-like
in plant cells or folding in animal cells. The cristae will increase in
number when the respiration rate inside the cell increases. There are
a lot of stalked granules embedded on the inner membrane.

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