Science Notes;
GENERAL SCIENCE -7
CHAPTER – 1 (PLANT SYSTEM)
Q.1. What
is photosynthesis?
Ans: The
process during which carbon dioxide and water
combine in the presence of sunlight and chlorophyll
to form glucose (food) and oxygen in leaf
is called photosynthesis.
Carbon dioxide + Water + Sunlight energy Food (Glucose) + Oxygen
Q.2. On what factors does photosynthesis
depend?
Ans. Photosynthesis
depends on the following factors:
Light Photosynthesis requires energy for combining carbon dioxide and water to form glucose (food). Sunlight provides this energy.
Carbon Dioxide If there is more amount of carbon dioxide in the air, the rate of photosynthesis will be fast
Water Water is also an essential requirement for photosynthesis. If it is not available the rate of photosynthesis will be affected and plant will produce less food.
Chlorophyll The process of photosynthesis cannot take place without
chlorophyll. It is only the chlorophyll which absorbs sunlight and makes
it usable in the photosynthesis process.
Temperature
Photosynthesis is also affected by temperature.
The suitable temperature for this process
is 25 – 35°C. At very high or very low temperatures,
the process of photosynthesis will slow down.
Q.3. What is meant by respiration?
Ans. Respiration
is defined as the process during which
glucose (food) reacts with oxygen to produce carbon dioxide, water and
energy required for survival
of life.
Respiration takes place in
mitochondria of all the cells of living bodies. Mitochondria
are called power house of the cell.
Respiration is the only process which
provides energy in usable form by living things.
Q.4. What is transpiration ?
Ans. Plants absorb water from soil through roots. Water is conducted to leaves where it is used in photosynthesis. The excessive water is removed through stomata and from the aerial parts of the plants. The loss of water from aerial parts of the plants is called transpiration.
Q.5. Describe importance of transpiration in plants?
Ans. Transpiration
pulls the water through air spaces in
spongy mesophyll and keeps the mesophyll moist,
which is essential for the exchange of gases.
Effects of evaporation of water from leaves
or stems are:
• cools the surface of the leaves and the surroundings as well
• allows the movement of minerals
from the soil to different parts of the plant
• helps in growth and development.
• controls the temperature of the plants.
Q.6. Which factors affect the rate of
transpiration?
Ans. Wind
Wind sweeps the humidity away from leaves
surroundings and increases the rate of transpiration.
Temperature Rise in temperature increases the rate of evaporation in the leaves surfaces.
This process increases the rate of
transpiration.
Light
In sunlight, the stomata remain open for removal of water through them. In this way light also affects the rate of transpiration.
Humidity
Humid air more amount of water and decreases
the rate of transpiration of water molecules
from plants leaves into air.
Q.7. Describe the root system.
Ans. Roots
are the underground parts of the plants which
absorb water and minerals from the soil. The initial root which grows from
radicle of the embryo is the
primary root or tap root. Its further branches
form secondary and tertiary root system.
Root tip is covered by hard and protective
structure called root cap. It protects the
newly born soft cells and enables root tip to grow
through soil. Root hairs are
thread-like which increase the
surface area for absorption of water.
Q.8. Describe internal structure of root.
Ans. The
main parts in the internal structure of root are
epidermis, cortex, endo-dermis vascular bundles.
Epidermis
It is an outermost layer of the root having root hairs. Epidermis provides protection and helps in absorption of water and
minerals from the soil.
Cortex Inside the epidermis, many layers of thin walled and rounded cells form cortex. Water and minerals absorbed by root hairs in epidermis are transported towards xylem through cortex for onward conduction to leaves
Endodermis The innermost layer of cortex which consists of barrel shaped cells is called endodermis. It regulates the movement of water and hormones, etc., into and out of the vascular system
Vascular system Xylem and phloem form vascular system. Xylem conducts water and minerals from roots to leaves through stem. Phloem transports food from leaves to roots and other parts of the plants.
Q.9. Describe shoot system of a plant.
Ans. The
outer parts of the plants such as stem, its branches,
leaves, flowers and fruit form shoot system.
Stem
Stem is the aerial part of the plant. It provides support to its branches, leaves, flowers and fruit,
etc. Xylem and phloem run through stem to
leaves for transport of material within the
plant body.
Leaves
Stem and its branches bear leaves. Leaves
are the organs which are well exposed to light and well adapted for preparation of food during photosynthesis. A leaf is
provided with the stalk called petiole.
Its flat green part is called blade
or lamina, which has many veins. The middle
strong vein is called midrib.
Q.10. What is diffusion?
Ans. Movement
of material particles from the area where
they are more, to the area where they are less
is called diffusion. The diffusion through membranes
(like cell membranes) is called osmosis.
As the concentration of water and dissolved minerals is more in soil as
compared to the root cells, they move in the root tissue (by osmosis). The xylem is a tissue in plants
which forms a system of pipelines (xylem vessels) from roots to leaves through stem for the
conduction of water, only in one direction.
Q.11. Define translocation.
Ans. Food
prepared by photosynthesis in leaves enters the
phloem in dissolved form. Phloem carries
from leaves to all parts of the
plan including roots. This
process of transportation of food to all
parts of the body is called translocation.
Q.12. What
is the role of Xylem and Phloem in plants?
Ans. Xylem and Phloem make vascular bundles in the plan.
Water and minerals diffuse from soil to roots
of the plant. These are conducted towards leaves
through stem by xylem. The food prepared
in leaves is transported to different parts
of the plant through phloem.
Q.13. What are stomata in the plant?
Ans. Stomata are tiny holes in the lower epidermis
of a leaf. A large number of stomata are
present in lower epidermis of
the leaf. Stomata help in absorption
of carbon dioxide and release of surplus
oxygen in the environment. Stomata help in
release of water in the environment. Stomata are
the features of leaf that facilitate photosynthesis.
Q.14. Describe
the adaptations in leaf structure for photosynthesis.
Ans. 1. The blades of leaves are flat and absorb maximum
light required for photosynthesis.
2. Thin blades
of leaves make the light and carbon
dioxide reach the internal parts easily.
3. Thick layer of palisade
mesophyll can make maximum
absorption of light to make food.
4. Maximum air spaces among
spongy mesophyll provide an easy passage
for carbon dioxide to diffuse
into cells containing chloroplasts to facilitate
photosynthesis.
5. Stomata in the lower epidermis
absorb maximum carbon
dioxide needed for photosynthesis.
6. Division of vascular bundles
into small branches spread throughout the
leaf makes an easy and maximum water supply needed for photosynthesis.
Q.15. How does a
plant get mineral from the soil?
Ans. Minerals
are the chemical substances required by
an organism for growth and other vital functions.
Carbon, hydrogen, oxygen, nitrogen, magnesium,
etc. are the nutrients required by plants
in large quantities. Nutrients like Magnesium
and Nitrogen are obtained from the soil
dissolved in water.
Q.16. Describe
the function of different minerals in the plant.
Ans. Minerals are important for growth of a plant. Some
important mineral are Magnesium, Nitrogen.
Magnesium It is
required by plants for the formation
of chlorophyll. It is helpful for the functioning
of enzymes to produce carbohydrates
and fats. Its deficiency causes poor
growth, yellowing and wilting of
leaves.
Nitrogen Nitrogen in the form of its compounds (nitrates), dissolved in soil water, is
required by plants for making
chlorophyll and amino acids. Amino
acids form proteins. Chlorophyll is necessary
for photosynthesis. Proteins are necessary
for growth, repair and other developments
and defensive functions.
Deficiency
of nitrogen makes the leaves pale green
or yellow and affects the rat of photosynthesis.
Q.17. Compare
photosynthesis and respiration.
Ans. Comparison and Contrast between Photosynthesis and Respiration
1. Photosynthesis takes place in green plants, algae and some bacteria, whereas,
respiration takes place in all
the living things.
2. Photosynthesis takes place in chloroplasts, whereas, respiration takes place in mitochondria.
3. Photosynthesis
uses sunlight energy to prepare
food, whereas, respiration releases energy
from food which is used for growth
and performing all other body
functions.
4. The products made during photosynthesis, i.e., glucose
and oxygen are the reactants of respiration.
5. The products of respiration, i.e., carbon dioxide and water are the reactants of photosynthesis.