Excretion (Edexcel IGCSE Science (Double Award): Biology): Flashcards
Exam code: 4SD0
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- FrontExcretion in Plants
Which two waste gases must leave a plant?
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Which two waste gases must leave a plant?
Oxygen
Carbon dioxide
Each can be both a reactant and a waste product, depending on the time of day.
Which gas is in excess during the day, and why?
Oxygen.
The rate of photosynthesis is higher than the rate of respiration, so more oxygen is produced than used.
Which gas is in excess at night, and why?
Carbon dioxide.
There is no photosynthesis, only respiration, so carbon dioxide is produced and none is used up.
Through which structures do waste gases leave a plant?
The stomata, in the leaf.
Why is excretion in plants not technically an active process?
Because the excess gases leave by diffusion, which requires no energy from the plant.
What happens to plant waste products that are not excreted?
Some are used up in other processes within the plant.
Which organ is responsible for excretion in a plant?
The leaf.
Waste gases diffuse out of a plant through the ＿＿＿＿＿＿＿＿ in the leaf.
Waste gases diffuse out of a plant through the stomata in the leaf.
During the day a plant excretes excess ＿＿＿＿＿＿＿＿, the waste product of photosynthesis.
During the day a plant excretes excess oxygen, the waste product of photosynthesis.
True or False?
Photosynthesis stops at night but respiration continues.
True.
With insufficient light there is no photosynthesis, only respiration, so carbon dioxide becomes the gas in excess.
True or False?
Oxygen is always a waste product in a plant.
False.
Oxygen is a waste product of photosynthesis but a reactant in respiration — which gas is in excess depends on the time of day.
During the day, why is less carbon dioxide released than used?
Because photosynthesis uses carbon dioxide faster than respiration produces it, so there is a net uptake of carbon dioxide.
Define excretion.
The removal of the waste substances of metabolic reactions, toxic materials, and substances in excess of requirements.
Name the metabolic wastes produced by the human body.
Carbon dioxide and water, from aerobic respiration in cells
Urea, from the breakdown of excess amino acids in the liver
Why is a build-up of carbon dioxide dangerous?
It dissolves easily in water to form an acidic solution, which lowers the pH of cells and can reduce enzyme activity.
What osmotic problem can a build-up of waste cause?
Body fluids become more concentrated, so water moves out of the cells by osmosis and essential reactions can no longer take place.
How does urea travel from the liver to the kidneys?
Dissolved in the blood plasma.
Name the three organs of excretion in humans.
Kidneys
Lungs
Skin
What do the kidneys excrete, and how?
Urea, water and excess ions, excreted in the urine.
What do the lungs excrete, and how?
Carbon dioxide and water as vapour, both leaving during exhalation.
What does the skin excrete, and how?
Excess mineral ions such as sodium, water, and some urea — all lost via sweating.
Where is urea produced?
In the liver, by the breakdown of excess amino acids.
The kidneys excrete urea, water and excess ions in the ＿＿＿＿＿＿＿＿.
The kidneys excrete urea, water and excess ions in the urine.
Excretion at the skin surface happens by ＿＿＿＿＿＿＿＿.
Excretion at the skin surface happens by sweating.
True or False?
Faeces is an example of excretion.
False.
Faeces consists mainly of undigested food, not waste from metabolism, so it is egestion, not excretion.
True or False?
Water is excreted by all three excretory organs.
True.
The kidneys excrete it in urine, the lungs as vapour in exhaled air, and the skin in sweat.
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