NCERT Class 11-Biology: Chapter –11 Transport in Plants Part 6

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Question 3:

From your knowledge of physiology can you think of some method of increasing the life of cut plants in a vase?

Answer:

Some methods that can increase the life of cut plants in a vase are:

(a) Using plant growth hormone called Cytokinins that help delay senescence or aging of plant parts.

(b)Placing the cut stem immersed in water in the vase to not allow water cavitation to occur by air.

(c) Essential oils can increase vase life of cut plants.

Question 4:

Do different species of plants growing in the same area show the same rate of transpiration at a particular time? Justify your answer.

Answer:

No, different species of plants growing in the same area does not show the same rate of transpiration at a particular time because the rate of transpiration also depends on internal factors like the morphological characteristics of a plant. For eg: Leaf area, thickness of cuticle, number of stomata and whether it is sunken or not etc. So upon these difference, the rate of transpiration is also dependent.

Question 5:

Water is indispensable for life. What properties of water make it useful for all biological processes on the earth?

Answer:

Properties of water that makes it useful for all biological processes on the earth are:(a) All polar substances are known to dissolve in polar solvents like water. All the essential substances in living organisms are solutes dissolved in water and transported from one place to another.

(b) Specific heat is the amount of heat required to increase the temperature of one gram of matter by one degree rise in temperature. Because of having high specific heat, it needs high amount of energy to increase its temperature. This is why living organisms have a constant temperature needed for metabolic processes in the body.

(c) Surface tension is the cohesion of the water molecules on the fluid surface of occupying the least volume. Viscosity is the resistance of a fluid to flowing water.

(d) Water expands when its temperature becomes lesser than 4◦C. This decreases its density and making ice float. This helps living organisms to survive in frozen oceans and lakes and the upper frozen layer prevents the whole water to freeze acting as an insulator.

(e) Water rises in capillary tubes which is a property that helps transport of water from roots of the plants to other parts of the plant.

Question 6:

How is it that the intracellular levels of K+ are higher than extracellular levels in animal cells?

Answer:

Intracellular levels of ions are maintained higher then extracellular levels in animal cells because animal cells have ATP powered pumps like the Na+- K+ pump where 3Na+ is sent out in exchange of 2 K+ ions thus increasing the level of K+ ions in the intracellular region. This is how via the pumps, ion concentration is maintained higher intracellularly than in extracellular region.

Question 7:

Cut pieces of beetroot do not leave colour in cold water but do so in hot water. Explain.

Answer:

Cut pieces of beetroot do not leave colour in cold water but do so in hot water because beetroot loses colour only when it is placed in hot water as the plasma membrane of the cells denatures at high temperature and breaks down leading to loss of content of cellwhich is the coloured protoplasm leaks out.

Question 8:

In a girdled plant, when water is supplied to the leaves above the girdle, leaves may remain green for some-time then wilt and ultimately die. What does it indicate?

Answer:

Girdling is the complete removal of a bark strip around the entire circumference of a trunk of a tree. In a girdled plant, when water is supplied to the leaves above the girdle, leaves may remain green for some time because leaves have the capability of synthesizing their own food by photosynthesis using water and from air. But will eventually die because water will slowly be unavailable thus no photosynthesis can occur.

Question 9:

Various types of transport mechanisms are needed to fulfil the mineral requirements of a plant. Why are they not fulfilled by diffusion alone?

Answer:

Simple diffusion is a kind of diffusion by which molecules are transported along the concentration gradient but too slowly. Also, not all kinds of molecules can pass through it. Only those which are non-polar and small can pass. But plants also require mineral nutrients and charged ions like potassium, sodium, etc. which cannot be transported via simple diffusion because the cell membrane which is selectively permeable does not allow large, polar and charged particles through. So processes like facilitated diffusion that used membrane proteins like carrier proteins and channel proteins aid in the exchange of required substances. These are specific and occurs along the concentration gradient. Even active transport is required to transport molecules against the concentration gradient. So to suffice the needs of the mineral requirements of the plant, only simple diffusion will not be enough.

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