B1T2 Revision Cards for Biology, Homeostasis

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  • Created by: Megnicpip
  • Created on: 31-03-16 15:48

Negative Feedback

It is a process that happens when your systems nned to slow down or completley stop a process that is happening.

Example include- when you eat the food travels to your stomach where digestio begins.You do not need your stomac working if you are not eating. The digestive system works with a series of hormones and nervous impulses to stop and start the secretion of acids in your stomach.

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Exam Question

Explain how the body maintains a stable internal temperature when the external temperature is 0'C

  • Vasconstriction is the process that happpens at 0'C because the temperature you have to git for this process to happen is 35'C.
  • What happens is the erector muscles contract pulling your hair upright to trap the warm air around you.
  • Your blood flows through more deeper vessels to protect your organs and not your nose, ears, hands etc.
  • The enzymes in your body are the catalysts and they are what give you goosebumps increasing the surface aea of your skin to keep you warmer.
  • Negative feedback controls what to do and when. It is like when your stomach does not need to work when you are not eating.
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Phototropism and Geotropism

Phototropism- plants grow towards light. Differential cell elongation causes stem to bend. Cells on the shaded side of a plant elongate.

Geotropism- roots grow down into soil

How do cells elongate?

  • An increase in cell wall activity (lower PH) activates the enzymes.
  • Auxin in higher concentration on shaded side of stem.
  • Only cells directly underneath stimulated cells elongate. Auxin in cytoplasm causes cell wall to acidify.
  • Water moves in by osmosis, swelling cell.
  • Cell wall has enzymes that loosen connections between cellulose when activated.
  • Cell membrane lays down additional cell wall material keeping new shape/size.
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Gibberellins

Gibberellins are defined as a class of plant hormones that stimulate growth stem and leaves, trigger the germination of the seed and breaking of bud dormancy, and stimulate fruit development with auxins.

When a seed grows the shoot grows upwards and the roots grow downwards. In the roots auxins cause cells to stop elongating and this causes positive geotropism. Therefore, the roots will grow in the direction of gravity. This helps to anchor the plant in place and helps the plant to collect water and nutrients.

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Diabetes

BMI= weight (kg) / height (m squared)

Type 1- pancreas does not prduce insulin. Inject insulin daily. Exercise and diet used to help lower glucose levels.

Type 2- cells respond less well to insulin. Control by changes in diet.

Risk Factors:

  • High fat
  • Lack of exercise
  • Age
  • Obesity
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