THREE MARKS QUESTIONS
11. Why is plasma membrane called selectively permeable membrane? How do substances like CO2 and water move in and out of the cell?
12. Explain hypotonic, isotonic and hypertonic solution. 13. Photoautotrophic bacteria lack chloroplast. Name the part of the bacterial cell which performs photosynthesis? Plants have large sized vacuole. Why?
14 Why are lysosomes known as scavengers of the cells? Give two functions of centrosome.
15. Give three similarities and one difference between mitochondria and plastid. Expand ATP.
Answers
Answer:
11. The cell membrane or the plasma membrane is known as a selectively permeable membrane because it regulates the movement of certain substances in and out of the cell. This means that the plasma membrane allows the entry of only some substances and prevents the movement of some other materials.
The cell membrane is selectively permeable and regulates the movement of substances in and out of the
cell.
Movement of CO2:
CO2 is produced during cellular respiration. Therefore, it is present in high concentrations inside the cell.
This CO2 must be excreted out of the cell. In the cell’s external environment, the concentration of CO2 is
low as compared to that inside the cell.
Therefore, according to the principle of diffusion, CO2 moves from a region of higher concentration
(inside the cell) towards a region of lower concentration (outside the cell).
Similarly, O2 enters the cell by the process of diffusion when the concentration of O2 inside the cell is low as compared to its surroundings.
Movement of water:
Water moves from a region of high concentration to a region of low concentration through the plasma membrane. The plasma membrane acts as a semi-permeable membrane, and this movement of water is known as osmosis. However, the movement of water across the plasma membrane of the cell is affected by the amount of substance dissolved in water.
12. If a cell is placed in a hypertonic solution, water will leave the cell, and the cell will shrink. In an isotonic environment, the relative concentrations of solute and water are equal on both sides of the membrane. When a cell is placed in a hypotonic environment, water will enter the cell, and the cell will swell.
13. Bacterial cell do not have chloroplast but yet some photoautotrophic bacteria perform photosynthesis due to the presence of chlorophyll in cooperated in the membrane. Embedded in the cell membrane are reaction centers which specifically absorb light energy.
Plant cells are known to have bigger vacuoles than that of animal cells as they need to store food and water. This is because the plant don't possess the ability to move freely like that of animals. Thus, they possess large vacuoles as a reservoir in unfavorable conditions.
14.Lysosomes are known as scavengers of the cell due to their ability of killing the dead cells of our body. They digest the dead cells or virus cells of out body and come out from our body through our excretory path.
Functions of centrosome:-
1). Centrosome organize the microtubules and provide a structure for the cell.
2). They also work to pull chromatids apart during the cell division.
15. Similarities
1. Both can produce their own copies by division.
2.mitochondria and plastics are they both are bounded with double membrane and they have there own gagnetic material.
3.They have their own dna and ribosomes. They have a double membrane.
difference
1. Mitochondria is the powerhouses cell.
plastids are the kitchen of the cell.
ATP stands for Adenosine Triphosphate
Answer:
THREE MARKS QUESTIONS
11. Why is plasma membrane called selectively permeable membrane? How do substances like CO2 and water move in and out of the cell?
12. Explain hypotonic, isotonic and hypertonic solution. 13. Photoautotrophic bacteria lack chloroplast. Name the part of the bacterial cell which performs photosynthesis? Plants have large sized vacuole. Why?
14 Why are lysosomes known as scavengers of the cells? Give two functions of centrosome.
15. Give three similarities and one difference between mitochondria and plastid. Expand ATP.