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What are tropisms?

A tropism is a growth in a plant in response to a stimulus. The stimulus could be a change in the direction of light or a water source. To recap, a stimulus is a change in the environment of an organism that...
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Answered by Holly P. • Biology tutor
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Explain the exchange of oxygen between an alveolus and a capillary.

The blood in the capillary has just returned to the lungs from the rest of the body, so contains a low concentration of oxygen. The alveolus contains air that has just been breathed in by ventilation, so it ...
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Answered by Anastasia D. • Biology tutor
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Using a diagram, outline the path the blood takes through the human body, starting with the aorta and identifying the major vessels and chambers of the heart.

Aorta --> systemic circulation [branches in order: coronary artery (to supply the heart), carotid artery (to supply the head), hepatic artery (to supply the liver), mesenteric artery (to supply the gut), ...
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Answered by Sophie G. • Biology tutor
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Gas exchange happens in the alveoli of the lungs. What are three adaptations of the alveoli that allow for this?

Thin alveolar walls for O2 and CO2 to travel through - To travel across the membrane, gases have to be dissolved, so the alveolar walls are moist - Large surface area to volume ratio allows for maximum gas e...
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Answered by Sarah L. • Biology tutor
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Describe the process of natural selection

There is genetic diversity within the population. Random mutation can occur, forming new alleles of a gene. Though many mutations are harmful, in certain environments the new allele may benefit its possessor...
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Answered by Jewel J. • Biology tutor
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