Cell: mitochondrion and plastid Flashcards
what is mitochondria
Mitochondria (sing.: mitochondrion), unless specifically stained, are not
easily visible under the microscope. The number of mitochondria per cell
is variable depending on the physiological activity of the cells. In terms of
shape and size also, considerable degree of variability is observed. Typically
it is sausage-shaped or cylindrical having a diameter of 0.2-1.0µm (average
0.5µm) and length 1.0-4.1µm.
how many membrane ,mitochondrionhas
Each mitochondrion is a double membrane-bound structure with the outer membrane and the inner
membrane dividing its lumen distinctly into two aqueous compartments, i.e., the outer compartment and the inner compartment
escribe the inner compaerment
The inner
compartment is filled with a dense homogeneous substance called the
matrix. The outer membrane forms the continuous limiting boundary of
the organelle. The inner membrane forms a number of infoldings called
the cristae (sing.: crista) towards the matrix (Figure 8.7). The cristae
increase the surface area. The two membranes have their own specific
enzymes associated with the mitochondrial function.
function of mitochondria
Mitochondria are
the sites of aerobic respiration. They produce cellular energy in the form
of ATP, hence they are called ‘power houses’ of the cell. The matrix also
possesses single circular DNA molecule, a few RNA molecules, ribosomes
(70S) and the components required for the synthesis of proteins. The
mitochondria divide by fission.
what are plastids
Plastids are found in all plant cells and in euglenoides. These are easily
observed under the microscope as they are large. They bear some specific
pigments, thus imparting specific colours to the plants. Based on the
type of pigments plastids can be classified into chloroplasts,
chromoplasts and leucoplasts
types of plastuds
The chloroplasts contain chlorophyll and carotenoid pigments which
are responsible for trapping light energy essential for photosynthesis.
In the chromoplasts fat soluble carotenoid pigments like carotene,
xanthophylls and others are present. This gives the part of the plant a
yellow, orange or red colour.
The leucoplasts are the colourless plastids
of varied shapes and sizes with stored nutrients:
Amyloplasts store
carbohydrates (starch), e.g., potato;
elaioplasts store oils and fats
aleuroplasts store proteins.
where are most of the choloroplasts found
Majority of the chloroplasts of the green
plants are found in the mesophyll cells of
the leaves. These are lens-shaped, oval,
spherical, discoid or even ribbon-like
organelles having variable length (5-10µm)
and width (2-4µm). Their number varies
from 1 per cell of the Chlamydomonas, a
green alga to 20-40 per cell in the mesophyll.
how many membranes does chloroplast have
the chloroplasts are
also double membrane bound. Of the two,
the inner chloroplast membrane is relatively
less permeable.
define:
i)stroma
ii) thylakoid
iii) grana/granum
iv) stroma lamellae
i) The space limited b the inner membrane of the chloroplast.The stroma of the chloroplast contains enzymes required for the
synthesis of carbohydrates and proteins.
ii) organised flattened membraneous structure present in the stroma.Chlorophyll pigments are
present in the thylakoids.
iii) stacks of thylakoids like piles of coins are called grana/granum/intergranal thylakoids.
iv) flatenned membraneous tubules connnecting thylakoids of different grana
what is lumen
The membrane of the thylakoids enclose a space called
a lumen.
choloroplasr is semi autonomous why
It also contains small, doublestranded circular DNA molecules and ribosomes. The ribosomes of the chloroplasts are smaller (70S)
than the cytoplasmic ribosomes (80S)
who discovered nucleus
Nucleus as a cell organelle was first described by Robert Brown as early
as 1831. Later the material of the nucleus stained by the basic dyes was
given the name chromatin by Flemming.
when is the nucleus clear
nucleus is most visible during interphase stage ( when the cell is not dividing)
how many membranes does nucelsu have? what is nucleuar envelope?
nucleus is a double membrane bound structure. nuclear envelope, which consists of two
parallel membranes with a space between
(10 to 50 nm) called the perinuclear
space, forms a barrier between the
materials present inside the nucleus and
that of the cytoplasm. The outer
membrane usually remains continuous
with the endoplasmic reticulum and also
bears ribosomes on it. At a number of
places the nuclear envelope is interrupted by minute pores, which are
formed by the fusion of its two membranes called nuclear pores.
function of nuclear pores?
These nuclear pores are the
passages through which movement of RNA and protein molecules takes
place in both directions between the nucleus and the cytoplasm.
