Tag:

aiims

Population Interactions – Competition

by Ramneet Kaur February 11, 2018

COMPETITION

Competition is the struggle between two or more organisms of same or different species for available resources.

Intraspecific competition is competition between individuals of same species. It is more acute as the requirements are same and can reduce the size of the population.

Interspecific competition is competition between individuals of different species. It occurs when organisms of different species have similar feeding habits. They belong to the same trophic level.

E.g., In grassland, there is competition between herbivores like rabbit, deer, bison.
Competition between resident fishes and visiting flamingoes for the zooplankton in the lake.
Carnivores like tiger and leopard compete for the same prey.
In forests trees, shrubs and herbs compete for water, minerals, and sunlight.

Ecology

Population Interactions

by Ramneet Kaur February 10, 2018

POPULATION INTERACTIONS

Population: the group of individuals of a species inhabiting a given area.
Habitat: it is the place where the organism lives. It is never occupied by a single species. It is occupied by a biological community.
Biological community: Populations of animals, plants, and microbes living in an area and interacting with each other.
Ecological niche: each species has a functional role to play in the ecological system.

Plant growth Plant physiology

VERNALIZATION

by Ramneet Kaur January 20, 2018

Vernalization

Vernalization is the effect of cold temperature on flowering.

It prevents precocious reproductive development late in the growing season and enables the plant to have sufficient time to reach maturity.
These plants remain vegetative during the warm season, receive low temperature during winter, grow further & then bear flower & fruits.

Lysenko 1^st reported the effect of cold temperature on flowering in the wheat seedling.

Plant growth Plant physiology

PHOTOPERIODISM

by Ramneet Kaur January 19, 2018

Photoperiodism

Photoperiodism is the effect of light on flowering.

Garner & Allard 1^st reported the effect of light on flowering in Maryland Mammoth (variety of tobacco) & Glycine max.
On the basis of photoperiodic requirements, plants are divided into 3 types:
Short day plants: in these plants, the dark period is very important for flowering. The dark period should exceed a critical length. Light has no effect on flowering. E.g., rice, sugarcane, potato, tobacco, soybean, Chrysanthemum.
Long day plants: in these plants, the light period is very important for flowering. The light period should exceed a critical length. Darkness has an inhibitory effect on flowering. E.g., wheat, oat, spinach, radish, barley, lettuce.
Day-neutral plants: these plants blossom throughout the year. Length of light or dark period has no effect. E.g., tomato, cucumber, sunflower, cotton, maize, pepper.

Plant growth Plant physiology

Abscisic acid

by Ramneet Kaur January 17, 2018

Abscisic acid:

Abscisic acid (ABA) is a growth inhibitor.

Discovered by 3 independent researchers as inhibitor-B, abscission II & dormin.They were chemically identical.
Addicott isolated it from cotton balls. Later renamed as abscisic acid.
Site of synthesis: chloroplast in leaves.
Translocated through phloem.
Formed by oxidation of carotenoids.

Plant growth Plant physiology

Ethylene

by Ramneet Kaur January 14, 2018

Ethylene:

Ethylene is a volatile gaseous compound that stimulates transverse growth but retards longitudinal growth.

Cousins confirmed its presence in ripened oranges, that hastened the ripening of stored unripe bananas.
Formed in all parts of the plant i.e., roots, leaves, flowers, seeds.
Maximum synthesis occurs in ripening fruits & tissues undergoing senescence.
Synthesized from Methionine.
Excess of auxin induces synthesis of ethylene.
Biologically active at low concentration.

Plant growth Plant physiology

CYTOKININ

by Ramneet Kaur January 12, 2018

Cytokinin:

Skoog & co-workers showed that callus formation occurred when internodal segments of tobacco are cultured. In the nutrient medium in addition to auxin, they provided extracts of yeast, vascular tissues, coconut milk or DNA.
Miller first discovered it from autoclaved Herring sperm DNA. He named it as kinetin.
Letham first obtained natural cytokinin from maize grain & coconut milk, it is referred as Zeatin.
Site of synthesis: Major source is roots & regions where rapid cell division occurs like meristems, root tip, buds, young leaves & developing fruits.
Transported through the xylem.
Derived from Adenine, it is 6-furfuryl aminopurine.

Plant growth Plant physiology

Gibberellins

by Ramneet Kaur January 11, 2018

Gibberellins

A Japanese farmer in his rice field found a seedling that is extremely tall, he named it as Bakanae means ‘foolish seedling’.
Kurosawa showed that it was due to an infection by fungus Gibberella fujikorai (Fusarium monoliforme).
Yabuta & Sumuki isolated it & named it as Gibberellins.
Chemically it is Gibberellic acid (C₁₉H₂₂O₆).
More than 100 different types of Gibberellins are known, of which GA₃ is the most common.
Precursor of gibberellins: Mevalonic acid (derived from Acetyl CoA).
Site of synthesis: shoot buds, young leaves & developing seeds.
Transported by simple diffusion.