A level Biology exam revision resources written by A level Examiners





 

'Growth is an increase in size, brought about by the addition of more body tissue.'

'Human growth is diffuse, which is in contrast to plant growth, which occurs at meristems.'

'Growth can be measured easily in 3 ways :

  • increase in mass
  • increase in height
  • increase in spine length
    (top of head to bottom of feet, when lying on the floor)'

Growth occurs during gestation, childhood and adolescence.

Growth rate = change in size per unit time, and when growth rates are plotted graphically the curves produced are called growth curves. Human growth curves show two growth spurts where the rate of growth is at its highest. One growth spurt lasts for the first two years of life, and is called the infant growth spurt. The other is linked to puberty and is called the pubertal growth spurt. This occurs earlier in girls than boys.

Allometric Growth is the differential growth of body parts. This causes our body proportions to change between infancy and adulthood.

Figure 1 : Cumulative (Total Growth)
Cumulative (Total Growth)

Figure 2 : Growth Rate
Growth Rate

Figure 3 : Differential Growth of different parts of the Body
Differential Growth of different parts of the Body


Gestation

Relatively short for humans because of our large brains and cranium mean longer gestation would cause birth problems.


Childhood

Pre-pubertal period gives us time to grow, develop and learn (acquire skills and knowledge). This phase is relatively longer in humans than in other animals (we have extended period of dependency). During childhood boys and girls grow at the same rate this growth is controlled by hormones. The pituitary gland secretes a hormone called pituitary growth hormone (PGH). Also it secretes a hormone called thyroid stimulating hormone (TSH) which stimulates the thyroid gland to secrete thyroxine. Thyroxine and PGH both stimulate growth.


Adolescence

During puberty the pituitary gland produces Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) which cause the ovaries to produce oestrogen and the testes to produce testosterone. These hormones are the sex hormones and cause the development of secondary sexual characteristics. The growth spurt that occurs during puberty is due to increased levels of PGH.




Figure 4 : The Control of Growth and Development
The Control of Growth and Development


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