Control and Coordination Part-3

Coordination in Plants

Plant Hormones

Hormones are responsible for coordinating and controlling in plants.

Plant Hormone 

 Function

Auxin

Helps in the growth of plant tissues, cell enlargement, cell maturation), breaks seed dormancy

Cytokinin

Promotes cell division, delays ageing of cells, helps in closing of stomata

Gibberellins

Helps in the growth of stems, initiates seed germination, promotes flowering, cell division and seed growth after germination

Ethylene

This is a gaseous hormone which causes the ripening of fruits

Abscisic acid

Inhibits growth and causes wilting of leaves, promotes dormancy of buds and seeds and causes premature falling of fruits and vegetables 

 

Plant Movements

  • Plants do not have a nervous system. Plants use chemical means for control and co-ordination.
  • Many plant hormones are responsible for various kinds of movements in plants.
  • Movements in plants can be divided into two main types : Tropic movement and Nastic movement

Tropic movement

  • The movements which are growth related are called tropic movements. These movements occur in response to environmental stimuli and the direction of the response is dependent on the direction of the stimulus.

Examples:

  • Phototropic movement (light-dependent)
  • Geotropic movement (gravity-dependent)
  • Chemotropic movement (chemical-dependent)
  • Hydrotropic movement (water-dependent)
  • Thigmotropic movement (touch dependent)

Geotropic movement

  • The growth in a plant part in response to earth’s gravitational force is called geotropic movement.
  • Towards gravity – positive geotropism
  • Away from gravity – negative geotropism
  •  Roots usually show positive geotropic movement, i.e. they grow in the direction of the gravity.
  • Stems usually show negative geotropic movement.

Phototropic Movement

  • The growth in a plant part in response to light is called phototropic movement.
  • Towards light-positive phototropism.
  • Away from light – negative phototropism.
  • Stems move towards the light, and roots move away from the light.

Hydrotropic movement

  • When roots grow in the soil, they usually grow towards the nearest source of water.
  • This shows a positive hydrotropic movement.
  • Towards water-positive hydrotropism.
  • Away from water – negative hydrotropism.
  • E.g. movement of roots towards high humidity level.

 

Chemotropism

  • The movement caused in plant in response to a chemical.
  • For example: growth of pollen tube.
  • As we see in case of pollen tube that it grows and enter the embryo sac through micropyle. This is actually in response to chemical.

Thigmotropic movement

  • The growth in a plant part in response to touch is called thigmotropism movement.
  • Towards touch – Positive thigmotropism.
  • Away from touch – negative thigmotropism.
  • Such movements are seen in tendrils of climbers.
  • The tendril grows in a way so as it can coil around a support. The differential rate of cell division in different parts of the tendril happens due to action of auxin.


Nastic Movement

  • The movements which are not growth related are called nastic movements.
  • These movements occur in response to environmental stimuli but the direction of response is not dependent on the direction of the stimulus.
  • The movement in the touch-me-not plant is thigmonastic movement (movement in response to touch).

Endocrine System in Humans

  • Exocrine Gland-They are glands that discharge secretions by means of ducts, which open onto an epithelial surface.
  • Endocrine Glands-They are the ductless glands which secrete hormones into the bloodstream in humans.
  • The endocrine glands present in the human body are the pituitary, thyroid, adrenal, pineal, pancreas, ovary (female), testis (male), etc.

 

Pituitary gland:

  • It is a pea-sized gland located at the in the midbrain.
  • It is also called the master gland of our body it controls the secretions of all the other endocrine glands.
  • The functioning of it is controlled by a part of the brain called the hypothalamus.
  • It also secretes Growth Hormone (GH). Under-secretion of GH causes Dwarfism, and over-secretion causes Gigantism in children and ‘Acromegaly’ in adults.

Thyroid Gland

  • It is butterfly-shaped bilobed gland located in the neck. It secretes thyroxine.
  • Thyroxin: Helps in controlling metabolism of fats, proteins and carbohydrates.
  • Iodine is required to synthesize thyroxine in the body.
  • In the case of iodine deficiency, under-secretion of thyroxine leads to goitre.
  • Malfunctioning of this gland causes thyroid in adults and cretinism in children.

Pancreas

  • It is located below the stomach.
  • It is the only gland that is endocrine as well as exocrine in function.
  •  Its endocrine part is ielts of langhams.
  • As an endocrine gland, it manufactures two hormones – Insulin and glucagon. Both these hormones act antagonistically and regulate the sugar level in the blood.
  • As an exocrine gland, it secretes enzymes to break down the proteins, lipids, carbohydrates and nucleic acids in food.
  • Deficiency of insulin from the pancreas leads to diabetes.

Adrenal Gland

  • It is located on the kidneys.
  • Occurs in pairs above each kidney.
  • It secretes adrenaline and corticoid.
  • Adrenaline helps in flight and fight response.

Gonads: Ovary and Testes

  • Gonads are the gamete-producing organs – testes in males and ovaries in females.
  • Ovaries: it is female gonad. It secretes oestrogen (female sex hormone): egg production, control sexual characters in females like widening of pelvic region, development of breast, pubic hairs etc.
  • It also secretes progesterone which controls pregnancy. It also helps in relaxing and in delivery.
  • Testis: it is male gonad. It secretes testosterone (male sex hormone): sperm production, also help in developing sexual characters in males. Like moustaches, beard, pubic hairs, widening of shoulders etc.