Plants can be classified based on their light requirements as heliophytes, which grow best in full sunlight, or sciophytes, which grow best in lower light intensities. Temperature affects many physiological processes in plants, such as increasing transpiration and the optimal rate for photosynthesis between 25-35°C. Topographic factors like altitude, slope, and direction of mountain chains influence regional climate and precipitation patterns, which in turn impact vegetation types and distributions. Rainfall determines the formation of biomes and vegetation types, and influences animal life through effects on habitat, metabolism, reproduction, and growth.

1. Prepared by –Anil Panchal
For- B.Sc. 2nd year Paper- I

13. Plant classification
Plants can be classified based on the requirement
of light:
• (a) Heliophytes grow best in full sunlight.
• (b) Sciophytes grow best at lower light intensity.
In comparison to the sciophytes, heliophytes
show thicker stems, more frequent branching,
smaller chloroplasts, roots longer, high
respiration rate, low water content, higher
concentration of salts and sugar, high osmotic
pressure etc.

21. Eco-phyiological responses of temperature
-
• Temperature is an ecological factor. It affects the rate of
many physiological processes in plants.
1. Transpiration: Rise in temperature increases transpiration
rate. High temperature influences the saturation deficit of
the atmosphere. It decreases the humidity of air. Thus
more water is transpired. High rate of transpiration also
increases the rate for absorption of water from the soil.
2. Photosynthesis: Photosynthesis occurs over a wide range
of temperature. In some desert plants photosynthesis
continues even at 80°C. Most of the algae require lower
temperature range for photosynthesis than the higher
plants. The optimum temperature for photosynthesis for
most of the plants is 25 to 35°C. Photosynthesis stops at
40°C in temperate plants and at 50°C in tropical plants
3. Respiration: The rate of respiration increases with the rise
of temperature. It is maximum at optimum temperature.
But it decreases rapidly above optimal temperature.

22. 4. General distribution of plants: Temperature and moisture
determine the general distribution of vegetation.
5. Germination of seed: Temperature also affects the
germination of seed. Every seed has optimal temperature.
Seed cannot grow below or above this temperature.
6. Spreading of diseases: Temperature and humidity affects the
spreading of plant diseases. Low temperature along with
high humidity favours the attack of rust. damping off,
seedling blight, foot rot and root rot.
7. Changes in the temperature in the natural environment of
plants affect both their functioning and their growth.
Maintenance of a relatively stable internal environment is
just as important for plant metabolism as it is for animals.
8. Leaf fall in Summer. Eucalypts are evergreen trees that drop
some of their leaves during the dry season in hot climates to
reduce the surface area exposed to absorb heat. This also
reduces the risk of losing too much water by transpiration.
9. Temperature is one factor that controls developmental
changes in a plant’s life cycle, from germination through to
flowering and seed dispersal.

25. Functions of Temperature:
1. Effect on metabolism: As temperature regulates the activity of enzymes, it
regulates the metabolic processes of organisms. It affects the rate of
transpiration, photosynthesis and seed germination in plants.
2. Effect on reproduction:
(a) Plants: Temperature affects flowering in plants. It also plays an important role in
the phenology (study of periodic phenomena) of plants.
(b) Animals: The maturation of gonads and liberation of gametes take place at a
particular temperature that varies from species to species. Breeding also is
affected in some due to temperature. The number of eggs laid by blowfly
increases with increasing temperature up to 32.5°C and thereafter decreases.
3. Effect on growth and development:
(a) Plants: Extremes of high and low temperature have adverse effect on the
growth of plants. Low temperatures bring about diseases like desiccation,
chilling and freezing injury. Extremely high temperature causes stunting and
death of plants — called heat injury.
(b) Animals: Growth and development of animals are affected by temperature.
Corals do not flourish when the temperature of water drops below 21°C. In
blow-fly, the incubation period of eggs decreases with increasing temperature.

26. 4. Effect on crossing over: Temperature is seen to affect the
crossing over and somatic expression of genes in animals. If
the larva or pupa are kept at low or high temperature it
affects the development of wings, eyes etc.
5. Effect on sex-ratio: In rotifers and daphnids, temperature
affects sex ratio. Under normal temperature, daphnids lay
parthenogenetic eggs that develop into females, while with
the increase in temperature they give fertilised eggs that
develop into either males or females.
6. Effect on colouration: Some species of mammals, birds and
insects present in warm humid climates, bear darker pigment
than the races of species who resides in cool and dry climate.
In Hyla (tree frog) and Phrynosoma (horned toad), low
temperature induces darkening of pigments.
7. Effect on morphology: The absolute size of an organism is
affected by temperature. Mammals and birds attain larger
body sizes in cold regions than in warmer areas. Whereas,
poikilotherms are smaller in cold regions.

39. Topographic Factors:
• The factors concerned with physical
geography of the earth are known as
topographic factors. These factors influence
vegetation which causes variation in climate of
a geographic region, ultimately give rise to a
characteristic microclimate.

40. The different topographic factors are:
1. Altitude of the place: As the altitude above the sea level increases, there
happens a decrease of temperature. Besides, the values of pressure,
humidity, wind velocity etc. also changes. All these factors together give a
definite pattern of vegetational zone.
2. Steepness and Exposure of the slope:
• The slope of mountain affects the nature of vegetation. In northern
hemisphere, south facing slopes receives more solar radiation than the
north facing slope. This may be due to the fact that the steep southern slope
receives the solar radiation almost at right angles during the mid-day
whereas the northern slopes receive only oblique rays during morning and
evening hours. This difference in solar radiation brings about a change in
vegetation in the two sides of the slope.
• In addition to this, the steepness of slope accelerates the downward
movement of surface water. The downward movement of water over the
slope causes soil erosion and as a result, the vegetation disappears from that
area.
3. Direction of mountain chains: The direction of mountain chains considerably
influences the rainfall in an area. If the mountain chains lie in the path of
wind full of water vapour, then there is heavy rainfall on the wind striking
side on the mountain chain.

43. Precipitation or rain falling on the earth’s surface
returns back to the atmosphere by two ways:
1. Some water is directly evaporated from the soil,
from open waters of ponds, lakes, oceans etc.
and from the surfaces of objects (wet from recent
rain).
2. Some water returns back via transpiration
(process by which the leaves of plants evaporate
water taken up from the soil by their roots).
The combination of the above two ways is referred
to as evapotranspiration

44. Functions of Rainfall
1. Formation of biomes: The annual amount of rainfall evenly
distributed in temperate latitudes determines the climax biotic
communities.
2. Type of vegetation: The annual rainfall determines the type of
vegetation. For example, heavy rainfall throughout the year in
tropical regions results in evergreen forest. Countries having heavy
rainfall in winter and less rainfall in summer results in the formation
of sclerophyllous forest—made of shrubs with leathery, thick
evergreen leaves. Conversely, areas with heavy rainfall during
summer and less in winter results in the formation of grassland.
3. Type of animals: With the change of vegetation due to rain, the
animal life also differs in different geographic regions.
4. Flooding and reactions by animals: Flooding by rainwater results in
dam building by beavers. Beaver’s dam contains felled trees, mud,
stones and sticks. Terrestrial vegetation in that area dies and
aquatic succession begins. Finally the beavers leave, the dam
deteriorates and breaks and the valley becomes a dry land again,
but with an altered soil consisting of the old lake bed.

45. 5. Effects on metabolism: Rainfall brings along with
it a cooling effect which regulates the activity of
various animals.
6. Effect on reproduction: Rainfall is one of the
physical factors that regulate the maturation and
liberation of gonads. For example, the croaking of
the male frog can be heard at the time of rainfall
which attracts the female for mating.
7. Effect on growth: In case of certain plants, the
advent of rainfall witnesses the appearance of
shoot and new leaves and branches.