3.
1 Homeostasis in Living Things
Homeostasis refers to the maintainance of the internal enviroment in the body of an
organism.
If the internal conditions are not balanced, for example the temperature is too high, the
cells of the organism may die.
Homeostatic Control Process
When the body temperature increases, the brain control centre will detect 察觉 the
changes and reduce 减少 to its normal range 范围
When the body temperature decreases, a corrective mechanism will take place and
the temperature will rise 上升 to its normal range.
Homeostasis is important to humans. Among the most important homeostasis in the
human body are the regulation of water and body temperature.
Regulation of water content
System that are involved in water regulation are the excretory system and endocrine
system. Examples of organs involved are kidneys and brain.
1. Water content in the body increases when we drink water
2. Detected by the brain
3. Corrective mechanism
- The brain will stimulate 刺激 the secretion 分泌物 of a hormone so that the
kidneys increase the production of urine
- More urine produced.
4. Water content in the body decreases.
1. Water content in the body decreases when we sweat 汗水
2. Detected by the brain.
3. Corrective mechanism
- The brain will stimulate the secretion of a hormone so that the kidneys will
decrease the production of urine.
- Feel thristy
4. Water content in the body increases.
Regulation of the Body Temperature
Systems that are involved in regulation of body temperature are the excretory system
and endocrine system. Examples of organs involved are skin, brain and skeletal
muscles.
1. During a hot day ,our body temperature will increase.
2. Detected by the brain
3. Corrective mechanism
- Blood vessels 血管 dilate 扩大
- Hairs lie flat
- Increase sweating 流汗
- Less urine
4. Body temperature decrease
Normal temperature ( 37C )
1. During a cold day, our body temperature will decrease.
2. Detected by the brain
3. Corrective mechanism
- Blood vessels constrict 收缩
- Hairs stand erect 树立
- Decrease sweating
- Skeletal muscles will contract and relax actively and it will cause an
individual 个人 to shiver 颤抖 to increase the body temperature. At the same
time, certain hormones will be secreted 分泌 to increase body metabolism 新
陈代谢
- Body temperature increases.
High surrounding temperature
- Hairs lie flat to reduce air trapped on the skin so that heat can be released
easily.
- Sweat glands 汗腺 produce more sweat to cool the skin when sweat is
evaporated.
- Blood vessels dilate 扩大 to let more blood flow close to the skin to increase
heat loss.
Low surrounding tempeature
- Erect 树立 hairs trap a layer of air that acts as a heat insulator
- Blood vessels constrict 收缩 to let more blood flow away from skin to reduce
heat loss.
Homeostasis in animals
Homeostasis also occurs in animals. Animals like cats and dogs do not have sweat
glands except on their sole. How do they maintain homeostasis during changes in
surrounding temperature?
Cats lick their fur to reduce their body temperature. Their furs stands erect when it is
cold to trap heat.
Dogs hang their tongue out so that the temperature decrease.
Snail : Loses a lot of water through evaporation on skin surface.
Produces fluid 液体 and looks for humid 潮湿 places to reduce water loss.
Bee : Has waxy 光滑 skin layer and loss of water vapour occurs through its spiracles
呼吸孔
Closes spiracles between two breathing movements to reduce water loss.
Lizards :
Cold surrounding :
- Body activities and movements become slower.
- Muscles function more slowly.
- Metabolism rate decreases.
- Body temperature decreases.
Hot surrounding :
- The heart beats faster.
- Movements become faster
- Metabolism rate increases.
- Body temperature increases.
Homeostasis in Plants
Water from plants are lost through a process known as transpiration. During
transpiration, plants lose water from leaves in the form of water vapour to the
surrounding through the stoma. The involves the transport system in plants.
- Transpiration helps plants to absorb and carry water and minerals from
the soil 土地 to all parts of the plants.
- Evaporation of water from the leaves cools the plant during hot days.
- Roots of plants absorb water and minerals from soil.
Stoma
Guard cells control the opening and closing of stoma.
During the day, stoma opens to enable exchange of gas. At the same time, water
vapour will be lost from the leaves and this will increase the rate of water intake 吸
入 by the roots. Stoma opens to enable more water to be evaporated from the
leaves through transpiration.
When the temperature is too high, stoma closes to reduce water evaporated from
the leaves through transpiration.
Importance of Homeostasis to Humans and Living Things
Homeostasis in human body and living things is to provide the optimum 最适宜的
conditions in the body so that cells can carry out metabolism activities efficiently
有效的.
We should be grateful that homeostasis enables the internal enviroment of our body to
be regulated and maintained in a balanced and stable condition.
