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What are the substances which organisms exchange with their environment?
Organisms exchange respiratory gases, nutrients, and heat (to maintain a constant body temperature) with their environment.
Which substances are exchanged between cells and their environment?
Cells take in oxygen and nutrients and excrete waste products like carbon dioxide and urea.
Give two reasons why diffusion across the outer membrane of multicellular organisms is too slow.
One reason why diffusion across the outer membrane of multicellular organisms is too slow is because some cells are deep within the body, so there is a big diffusion distance.
Another reason is that large animals have a low surface area to volume ratio.
Describe how the size of an organism affects its heat loss.
The larger the organism, the slower the rate of heat loss.
This is because the organism has a smaller surface area to volume ratio.
Explain why smaller organisms need a relatively high metabolic rate.
Smaller organisms need a relatively high metabolic rate to generate enough heat to stay warm.
This is because they have a large surface area to volume ratio, so they have a fast rate of heat loss.
Describe how the shape of an organism affects its heat loss.
The more compact the organism’s shape is, the slower the rate of heat loss.
This is because the organism has a smaller surface area
Describe an adaptation of a small desert mammal to aid exchange.
One adaptation of a small desert mammal to aid exchange is that they produce less urine.
This is because they lose more water from their surface, as they have a high surface area to volume ratio.
Describe three adaptations of a small mammal living in cold regions to aid exchange.
One adaptation of a small mammal living in cold regions to aid exchange is that they eat high-energy foods. This is to support their high metabolic rates.
Another adaptation is the small mammal hibernating.
Another adaptation is the small mammal having thick layers of fur.
Describe two adaptations of a large mammal living in hot regions to aid exchange.
One adaptation of a large mammal living in hot regions is that they will spend much of their day in water to lose heat.
Some large mammals will have large flat ears, which increases their surface area so more heat is lost.
Describe how single-celled organisms exchange gases.
Single-celled organisms exchange gases across their body surface by diffusion.
Explain why single-celled organisms do not need gas exchange systems.
Single-celled organisms do not need gas exchange systems because they have a large surface area, thin surfaces, and a short diffusion pathway.
What do insects use to exchange gases?
Insects use microscopic air-filled pipes called tracheae to exchange gases.
What do the tracheae branch off into?
The tracheae branch off into smaller tracheoloes.
These have thin, permeable walls and go to individual cells.
Describe the movement of oxygen in an insect.
In an insect, oxygen moves into the tracheae through pores on the surface called spiracles.
Oxygen travels down the concentration gradient, through the tracheoles. It then reaches individual cells.
Oxygen diffuses directly into the respiring cells.
Describe the movement of carbon dioxide in an insect.
In an insect, carbon dioxide from the cells diffuses down its concentration gradient through the spiracles to be released into the atmosphere.
Describe how insects move air in and out of their spiracles.
Insects use rhythmic abdominal movements to move air in and out of their spiracles.
Describe three adaptations insects have to prevent water loss.
To prevent water loss, insects close their spiracles using muscles.
Insects also have a waterproof waxy cuticle all over their body.
Insects also have tiny hairs around the spiracles.
These prevent evaporation of water.
Briefly describe how water moves through a fish.
Water enters the fish through its mouth and passes through the gills.
Describe the structure of a fish gill, explaining how each component helps with the exchange of gases.
A fish gill is made of many thin plates called gill filaments, which give a large surface area.
The gill filaments are covered in lamellae, further increasing the surface area.
The lamellae have many blood capillaries and a thin surface layer of cells to increase the rate of diffusion.
Describe the counter-current system in a fish.
The counter-current system in a fish involves the blood flowing through the lamellae in one direction.
The water flows over the lamellae in the opposite direction.
The blood entering the lamella has a low oxygen concentration.
Why is the counter-current system important in fish?
The counter-current system is important in fish as it maintains a large concentration gradient between the water and the blood.
Explain why oxygen diffuses from the water into the fish's blood.
Oxygen diffuses from the water into the fish's blood because the concentration of oxygen in the water is always higher than the concentration of oxygen in the blood.
What do plants need carbon dioxide for?
Which waste gas is produced?
Plants need carbon dioxide for photosynthesis, which produces oxygen as a waste gas.
What do plants need oxygen for?
Which waste gas is produced?
Plants need oxygen for respiration, which produces carbon dioxide as a waste gas.
What is the main gas exchange surface in the leaf?
Explain how it is adapted for efficient exchange.
The main gas exchange surface in the leaf is the surface of the mesophyll cells.
These have a large surface area.
How do gases move in and out of the plant?
Gases move in and out of the plant through special pores in the epidermis called stomata.
Describe how the stomata work.
The stomata can open to allow the exchange of gases.
The stomata can close if the plant is losing too much water.
Guard cells control the opening and closing of stomata.
Describe how the guard cells open and close the stomata.
The stomata opens when water enters the guard cells, making them turgid.
If the plant starts to get dehydrated, the guard cells lose water and become flaccid. This closes the stomata.
What is a xerophyte?
A xerophyte is a plant adapted for life in warm, dry, or windy habitats where water loss is frequent.
Give five examples of xerophytic adaptations.
Five examples of xerophytic adaptations include stomata sunk in pits, epidermal hairs, curled leaves, a reduced number of stomata, and waxy, waterproof cuticles.
Explain the purpose of stomata sunk in pits.
Stomata sunk in pits trap moist air.
This reduces the concentration gradient of water between the leaf and the air.
This reduces the volume of water diffusing out of the leaf and evaporating away.
Explain the purpose of epidermal hairs.
Epidermal hairs trap moist air around the stomata.
Explain the purpose of curled leaves.
Curled leaves protect the stomata from wind.
This is because windy conditions increase the rate of diffusion and evaporation.
Explain the purpose of a reduced number of stomata.
A reduced number of stomata means there are fewer places for water to escape.
Explain the purpose of waxy, waterproof cuticles.
Waxy, waterproof cuticles on leaves and stems reduce evaporation.
Describe the gross structure of the human gas exchange system.
The human gas exchange system begins with the trachea, which splits into two bronchi.
One bronchus leads to each lung.
Each bronchus branches off into bronchioles.
The bronchioles end in small air sacs called alveoli
What is the alveolar epithelium?
The alveolar epithelium is a single layer of thin and flat cells.
It surrounds each alveolus.
Describe four ways the alveoli are adapted for efficient exchange.
The alveolar epithelium is one cell thick.
There is a large number of alveoli in the lungs, which means there’s a large surface area.
The alveoli are surrounded by a network of capillaries, which maintain a steep concentration gradient by the flow of blood.
The alveoli are ventilated.
Describe the movement of oxygen in the alveoli.
Oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium.
The oxygen diffuses into haemoglobin in the blood.
Describe the movement of carbon dioxide in the alveoli.
Carbon dioxide diffuses into the alveoli from the blood.
It is then breathed out.
What does ventilation consist of?
Ventilation consists of inspiration and expiration.
Describe the first step of inspiration.
In the first step of inspiration, the external intercostal and diaphragm muscles contract.
This causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thoracic cavity.
Describe the second step of inspiration.
In the second step of inspiration, the lung pressure decreases as the volume of the thoracic cavity increases.
The lung pressure decreases to below atmospheric pressure.
Air flows down the trachea and into the lungs down a pressure gradient.
True or false.
Inspiration is an active process.
True.
Inspiration is an active process.
Describe the first step of expiration.
In the first step of expiration, the internal intercostal muscles contract and the diaphragm muscles relax.
This causes the ribcage to move downwards and inwards and the diaphragm to become curved, decreasing the volume of the thoracic cavity.
Describe the second step of expiration.
In the second step of expiration, the lung pressure increases as the volume of the thoracic cavity decreases.
The lung pressure increases to above atmospheric pressure.
Air is forced out of the lungs down a pressure gradient.
What key word describes the interaction between the external and internal intercostal muscles?
The interaction between the external and internal intercostal muscles is antagonistic.
What happens to large biological molecules during digestion?
During digestion, large biological molecules are hydrolysed into smaller molecules that can be absorbed across cell membranes.
What is amylase?
Amylase is a digestive enzyme that catalyses the conversion of starch into maltose.
This involves the hydrolysis of the glycosidic bonds in starch.
Where is amylase produced and released?
Amylase is produced by the salivary glands (released in the mouth) and by the pancreas. (released in the small intestine)
What are membrane-bound disaccharidases?
Membrane-bound disaccharidases are enzymes that are attached to the cell membrane of epithelial cells lining the ileum.
They break down disaccharides into monosaccharides.
This involves the hydrolysis of glycosidic bonds.
What is lipase?
Lipase is a digestive enzyme that catalyses the breakdown of lipids into monoglycerides and fatty acids.
This involves the hydrolysis of the ester bonds in lipids.
Where are lipases made and released?
Lipases are made in the pancreas and released in the small intestine.
Where are bile salts produced?
Bile salts are produced by the liver.
Explain what bile salts do.
Bile salts emulsify lipids, causing them to form small droplets.
This increases the surface area of lipids available for lipases to work on.
What happens once the lipid has been broken down?
Once the lipid has been broken down the monoglycerides and fatty acids stick with the bile salts to form micelles.
What are endopeptidases?
Endopeptidases are digestive enzymes which hydrolyse internal peptide bonds within a protein.
Give three examples of endopeptidases.
Include where they are made and released.
Trypsin and chymotrypsin are two examples of endopeptidases.
They are made in the pancreas and released into the small intestine.
Pepsin is another endopeptidase. It is made in cells in the stomach lining and released into the stomach.
How are the optimum conditions of pepsin provided?
The optimum conditions of pepsin are acidic conditions, provided by hydrochloric acid in the stomach.
What are exopeptidases?
Exopeptidases are digestive enzymes which hydrolyse peptide bonds at the end of protein molecules.
They remove single amino acids from proteins.
What are dipeptidases?
Dipeptidases are exopeptidases that work specifically on dipeptides.
They act to separate the two amino acids by hydrolysing the peptide bond between them.
Where are dipeptidases often located?
Dipeptidases are often located in the cell-surface membrane of epithelial cells in the small intestine.
Describe how amino acids are absorbed by cells lining the ileum of mammals.
Amino acids are absorbed by cells lining the ileum of mammals via co-transport, through sodium-dependent transporter proteins.
Describe how different monosaccharides are absorbed by cells lining the ileum of mammals.
Glucose and galactose are absorbed by cells lining the ileum of mammals via a co-transporter protein.
Fructose is absorbed via facilitated diffusion through a carrier protein.
What do micelles contain?
Micelles contain bile salts, fatty acids, and monoglycerides.
Describe two things micelles do to fatty acids and monoglycerides.
Micelles make fatty acids and monoglycerides more soluble in water.
They bring the fatty acids and monoglycerides to cells lining the ileum, which maintains a higher concentration of fatty acids and monoglycerides in the cells.
Describe how fatty acids and monoglycerides are absorbed by cells lining the ileum of mammals.
Fatty acids and monoglycerides are absorbed by cells lining the ileum of mammals by diffusion.
What happens to the fatty acids and monoglycerides after they have been absorbed?
After the fatty acids and monoglycerides have been absorbed, they are reformed into triglycerides in the cells.
Vesicles move to the cell membrane and transport them out.
