Kerala SSLC Class 9 Solutions for biology – The Mystery of Growth (English Medium)
Page No. 58:
Does the body grow due to the growth of cells?
Or does it happen when the number of cells increases?
Growth of the body occurs when the number of cells increases.
How do the changes that occur in the cells lead to growth?
Changes occur when a cell is attaining a particular maturity level. These changes are duplication of the cytoplasm, cell organelles and nuclear material. These changes prepare the cell for multiplication, resulting in an increase in the number of cells and thus ultimately resulting in growth.
What is the role of cells in the growth of the body?
Cells play the most important role in the growth of the body. Growth in size of cells till maturity and division of cells to increase the number of cells are the key events which are responsible for the growth of the body.
Damaged and old cells are replaced by the division of cells.
Page No. 60:
What happens to the chromatin reticulum just before cell division?
- Just before cell division, the cell prepares itself for division.
- The long, thin thread-like chromatin reticulum becomes short and thick, forming chromosomes.
- These chromosomes duplicate and the chromatids are visible.
How does the structure of chromosome differ from that of chromatin reticulum?
The chromosomes are short and thick as compared to long, thin, thread-like chromatin reticulum.
In chromosomes, chromatids and centromeres are visible.
How is the chromosome related to gene?
Each chromosome carries a single DNA molecule, and the gene is a part of the DNA molecule which is responsible for carrying the characters.
How many chromosomes are there in the mother cell? What changes do they undergo?
There are two chromosomes in the mother cell in the given figure.
Before cell division, the chromosomes replicate producing exact duplicate copies of them.
What are the parts disappearing from the nucleus during division?
During division, the nuclear membrane and nucleolus of the nucleus disappear.
What is the function of spindle fibres?
Spindle fibres attach the centromere of the chromosome to the two poles of the cell. They help the sister chromatids of the chromosomes to separate and get pulled at opposite poles of the cell during cell division.
How many chromosomes are there in the daughter nucleus?
The daughter nucleus has the same number of chromosomes as the mother nucleus, i.e. each daughter cell has two chromosomes.
Page No. 61:
Is the division of the cytoplasm same as that of the nucleus?
Division of the cytoplasm is much simpler as compared to that of the nucleus.
When two copies of the nucleus are formed in the cell, a furrow is developed between the two nuclei exactly in the middle of the cell.
The furrow develops from the periphery towards the centre of the cell.
The furrow deepens and eventually forms two separate cells, each carrying a single daughter nucleus.
Is the process of cytoplasmic division similar in plant and animal cells?
Cytoplasmic division is different in plants and in animal cells.
In animal cells, a furrow is developed at the middle of the cell separating the two nuclei and forming two cells.
In plant cells, a cell plate is formed between two daughter nuclei. The cell plate elongates from the centre towards the periphery, eventually resulting in the formation of two daughter cells.
Page No. 63:
Is the growth of human beings and that of plants alike?
What differences do you come across?
Growth is very different in plants and in human beings.
Growth of a plant occurs throughout its lifetime; on the other hand, growth in human beings occurs only till the early twenties.
Growth occurs in all parts of the human body, whereas it is localised to certain parts, i.e. meristematic tissues only, in plants.
Observe the given figures a and b, find out the differences between a meristematic cell and a mature cell and complete the table.
Page No. 64:
Do you know where the meristems are found?
Meristems are found at the following parts of the plant:
- Apical meristem:
• Tip of the root
• Tip of the stem
- Lateral meristem:
• Present laterally in the stem and roots of dicot plants
- Intercalary meristem:
• Above nodes in monocotyledonous plants
• On the sides of the stem or root in dicotyledonous plants
Page No. 65:
Compare the position and function of different types of meristems.
Why don’t monocotyledonous plants increase in girth like that of dicotyledonous plants?
Monocotyledonous plants do not have lateral meristematic tissue which helps increase the girth of dicotyledonous plants. Hence, monocotyledonous plants do not show increase in girth like dicotyledonous plants.
Page No. 66:
Do microorganisms grow like plants and animals?
Microorganisms are unicellular organisms. They do not grow like plants and animals. They grow in cell size for a cell division which is to fulfill the purpose of reproduction. However, post-division, they do not form tissues like plant and animal cells but survive as individual organism.