Cell Structure
Chapter - 1
A' Level
Q/A
Q.1. What is protoplasm?
Ans: A cell is a unit of life. It consists of a mass of living matter called protoplasm. Protoplasm is a complex jelly-like substance in which endless chemical activities are carried out that ensure the life of a cell.
Q.2. What is cell biology?
Ans: The study of cells has given rise to an important branch of biology known as cell biology.
Q.3. Name the structures that animal and plant cells have in common, those found in only plant cells, and those found only in animal cells.
Ans: In animals and plants each cell is surrounded by a very thin cell surface membrane. This is also sometimes referred to as the plasma membrane.
Many of the cell contents are colourless and transparent so they need to be seen. Each cell has a nucleus, which is a relatively large structure that stains intensely and is therefore very conspicuous. The deeply staining material in the nucleus is called chromatin and is a mass of loosely coiled threads.
Mitochondria are only just visible, but films of living cells, taken with the aid of a light microscope, have shown that they can move about, change shape and divide.
Each cell has a nucleus, which is a relatively large structure that stains intensely and is therefore very conspicuous. The deeply staining material in the nucleus is called chromatin and is a mass of loosely coiled threads.
Differences between animal and plant cells:
* Plant cells are often larger than animal cells, although cell size varies enormously.
* With a light microscope, individual plant cells are more easily seen than animal cells, because they are usually larger and unlike animal cells, surrounded by a cell wall outside the cell surface membrane.
* Vacuoles are not confined to plant cells; animal cells may have small vacuoles, such as phagocytic vacuoles, although these are not usually permanent structures.
Chloroplasts are found in the green parts of plant.
Units of measurement:
one-thousandth = 0.001 mm
one millionth = 0.000 001 micrometre
one thousand millionth = 0.000 000 001 nanometre
Calculating the magnification of a photograph or image:
Magnification is the number of times larger an image is, than the real size of the object.
Magnification = observed size of the image/ actual size
M = I / A
Here, I = observed size of the image
A = actual size
Suppose we want to know the magnification of the plant cell labelled in the figure. If we know its actual length we can calculate its magnification using the formula
Step - 1:
Measure the length in mm of the cell in the photograph using a ruler. It is about 60 mm.
Step - 2:
Convert mm to μm
1 mm = 1000 μm
60 mm = 60 X 1000 μm
= 60,000 μm
Step - 3:
Use the equation to calculate the magnification.
magnification, M = image size, I / actual size, A
= 60,000 μm / 80 μm
= x 750
Q.4. a) Calculate the magnification of the drawing of the animal cell in the figure -1.
b) Calculate the actual length of the chloroplast labeled in the figure - 2.
The structure of the chloroplast as seen with the electron microscope is visible. Chloroplasts tend to have an elongated shape and a diameter of about 3 to 10 micro m.
The second stage of photosynthesis ( the light-independent stage) uses the energy and reducing power generated during the first stage to convert CO2 into sugars. This requires a cycle of enzyme-controlled reactions called the Calvin cycle and takes place in solution in the stroma. The sugars made may be stored in the form of starch grains in the stroma. The lipid droplets also seen in the stroma as black spheres in electron micrographs are reserves of lipid for making membranes or from the breakdown of membranes in the chloroplast.
Q.5. What is resolution?
Ans: resolution is the ability to distinguish between two objects very close together; the higher the resolution of an image, the greater the detail that can be seen.
Q.6. What is magnification?
Ans: Magnification is the number of times greater that an image is than the actual object;
magnification = image size / actual size of the object