A Body at Rest Is Still Working Around the Clock
See why the life processes cannot pause even during sleep, write and explain the photosynthesis equation with the role of stomata, compare the four kinds of nutrition, and follow food through the alimentary canal enzyme by enzyme.
Why can the life processes never take a break?
Watch someone asleep and nothing seems to be happening. No movement, no eating, no visible effort. Yet they are breathing, their heart is beating, their kidneys are working, and they will be hungry when they wake.
The reason is that being alive is not a state but a continuous repair job. The molecular structures a body is built from — cell membranes, proteins, tissues — wear out and break down all the time, simply because they are made of matter and matter is disturbed by its surroundings. If the rebuilding stopped, the structures would come apart, and the organism would stop being an organism.
So energy is needed even when nothing is being done with it, and that energy has to come from outside. That is why nutrition and respiration continue during sleep, and it is the honest answer to the question why must life processes go on even when an organism is at rest.
The processes that keep this going are called the life processes:
- Nutrition — taking in and using food for energy and materials
- Respiration — releasing energy from that food
- Transport — carrying food, oxygen and wastes to where they are needed
- Excretion — removing the harmful by-products
A single-celled organism needs no special organs for any of this: its whole surface is in contact with the environment, so food, oxygen and waste can all pass straight across. A large multicellular body cannot do that, because most of its cells are nowhere near the surface — and that is why plants and animals have specialised organs and transport systems at all.
This page covers the first part of the CBSE Class 10 Science chapter on life processes: the life processes and maintenance, photosynthesis, the types of nutrition, and human digestion.
The reason is that being alive is not a state but a continuous repair job. The molecular structures a body is built from — cell membranes, proteins, tissues — wear out and break down all the time, simply because they are made of matter and matter is disturbed by its surroundings. If the rebuilding stopped, the structures would come apart, and the organism would stop being an organism.
So energy is needed even when nothing is being done with it, and that energy has to come from outside. That is why nutrition and respiration continue during sleep, and it is the honest answer to the question why must life processes go on even when an organism is at rest.
The processes that keep this going are called the life processes:
- Nutrition — taking in and using food for energy and materials
- Respiration — releasing energy from that food
- Transport — carrying food, oxygen and wastes to where they are needed
- Excretion — removing the harmful by-products
A single-celled organism needs no special organs for any of this: its whole surface is in contact with the environment, so food, oxygen and waste can all pass straight across. A large multicellular body cannot do that, because most of its cells are nowhere near the surface — and that is why plants and animals have specialised organs and transport systems at all.
This page covers the first part of the CBSE Class 10 Science chapter on life processes: the life processes and maintenance, photosynthesis, the types of nutrition, and human digestion.
What exactly happens during photosynthesis?
Green plants use light energy to build carbohydrate from carbon dioxide and water, releasing oxygen.
Check that the equation balances: carbon and ; hydrogen and ; oxygen on the left and on the right. And note that sunlight and chlorophyll go above the arrow — chlorophyll is not consumed and sunlight is not a substance, so neither belongs among the reactants.
The three events, in order.
- Absorption of light energy by chlorophyll in the chloroplasts
- Conversion of light energy into chemical energy, and the splitting of water into hydrogen and oxygen. The oxygen released into the air comes from this step, from water and not from carbon dioxide
- Reduction of carbon dioxide to carbohydrate, using that hydrogen
These steps need not happen one immediately after the other, and that is a point the syllabus makes explicitly. In some plants the carbon dioxide is taken in at night and stored, and the carbohydrate is built during the day.
The three raw materials and where each comes from.
- Carbon dioxide from the air, entering through the stomata
- Water from the soil, drawn up by the roots
- Minerals such as nitrogen, phosphorus, iron and magnesium, absorbed from the soil and used to build proteins and other components
How the stomata control the trade-off. Stomata are tiny pores in the leaf surface, each bounded by two guard cells. When water flows into the guard cells they swell and the pore opens; when water leaves, they shrink and the pore closes.
And the closing matters as much as the opening. A wide-open pore lets carbon dioxide in — and lets water vapour out. So stomata are kept closed when carbon dioxide is not needed, which is how a plant limits its water loss. That is why leaves have most of their stomata on the lower surface, away from direct sun, and why a plant short of water wilts and stops photosynthesising.
The observation that ties it together. Cover part of a leaf with black paper, leave the plant in sunlight, then test the leaf with iodine: the covered part gives no blue-black colour because no starch was made there. Light is necessary, and the starch test proves it — a genuine experiment and not an assertion.
Check that the equation balances: carbon and ; hydrogen and ; oxygen on the left and on the right. And note that sunlight and chlorophyll go above the arrow — chlorophyll is not consumed and sunlight is not a substance, so neither belongs among the reactants.
The three events, in order.
- Absorption of light energy by chlorophyll in the chloroplasts
- Conversion of light energy into chemical energy, and the splitting of water into hydrogen and oxygen. The oxygen released into the air comes from this step, from water and not from carbon dioxide
- Reduction of carbon dioxide to carbohydrate, using that hydrogen
These steps need not happen one immediately after the other, and that is a point the syllabus makes explicitly. In some plants the carbon dioxide is taken in at night and stored, and the carbohydrate is built during the day.
The three raw materials and where each comes from.
- Carbon dioxide from the air, entering through the stomata
- Water from the soil, drawn up by the roots
- Minerals such as nitrogen, phosphorus, iron and magnesium, absorbed from the soil and used to build proteins and other components
How the stomata control the trade-off. Stomata are tiny pores in the leaf surface, each bounded by two guard cells. When water flows into the guard cells they swell and the pore opens; when water leaves, they shrink and the pore closes.
And the closing matters as much as the opening. A wide-open pore lets carbon dioxide in — and lets water vapour out. So stomata are kept closed when carbon dioxide is not needed, which is how a plant limits its water loss. That is why leaves have most of their stomata on the lower surface, away from direct sun, and why a plant short of water wilts and stops photosynthesising.
The observation that ties it together. Cover part of a leaf with black paper, leave the plant in sunlight, then test the leaf with iodine: the covered part gives no blue-black colour because no starch was made there. Light is necessary, and the starch test proves it — a genuine experiment and not an assertion.
How do the four kinds of nutrition differ?
Autotrophs make their own food; heterotrophs take it from elsewhere, and they do so in three different ways.
Autotrophic nutrition. The organism builds its own food from simple inorganic substances using an outside energy source. Green plants and some bacteria do this, storing the carbohydrate as starch in plants and as glycogen in animals and fungi.
Heterotrophic nutrition covers everything else, and splits into three:
Holozoic — the whole food is taken in, digested inside the body, and the undigested part thrown out. Humans, most animals and Amoeba all feed this way.
Amoeba is the syllabus example worth describing. It has no mouth. It pushes out temporary finger-like extensions called pseudopodia, which surround the food particle and fuse over it, enclosing it in a food vacuole. Enzymes inside the vacuole digest it, the useful products pass into the cytoplasm, and the residue is thrown out when the vacuole meets the surface. Paramoecium does the same job differently, using cilia to sweep food to a fixed point on its surface.
Saprophytic — the organism secretes digestive juices onto dead and decaying matter and then absorbs the dissolved products. Bread mould, yeast, mushrooms and Rhizopus feed this way. The digestion happens outside the body, which is the defining feature, and it is why a patch of mould spreads across bread rather than swallowing it.
Parasitic — the organism takes its food from the body of another living organism, the host, usually without killing it immediately. Cuscuta, also called amarbel, is a plant parasite that has no chlorophyll and draws its food from the plant it climbs on. Ticks, lice, leeches, roundworm and the malarial parasite are animal examples.
Worked classification. Classify a mushroom, a leech, a mango tree and an Amoeba.
- Mushroom — saprophytic, since it lives on dead organic matter and digests outside itself
- Leech — parasitic, since it feeds on a living host
- Mango tree — autotrophic, since it photosynthesises
- Amoeba — holozoic, since it takes in whole food particles
The distinction most often blurred. Saprophytes and parasites both live on other organisms, but a saprophyte needs its source to be dead while a parasite needs it to be alive. So a fungus on a rotting log is a saprophyte; the same kind of fungus growing on a living tree and harming it is a parasite. The state of the food source decides the name, not the organism.
A boundary case that is genuinely interesting. Some plants are green and photosynthesise, and also trap insects — the pitcher plant is the syllabus example. It cannot get enough nitrogen from the soil where it grows, so it obtains that one nutrient from the insect while making its carbohydrate itself. An organism can be autotrophic for energy and heterotrophic for a particular nutrient, which is why classification schemes describe the usual case rather than an absolute rule.
Autotrophic nutrition. The organism builds its own food from simple inorganic substances using an outside energy source. Green plants and some bacteria do this, storing the carbohydrate as starch in plants and as glycogen in animals and fungi.
Heterotrophic nutrition covers everything else, and splits into three:
Holozoic — the whole food is taken in, digested inside the body, and the undigested part thrown out. Humans, most animals and Amoeba all feed this way.
Amoeba is the syllabus example worth describing. It has no mouth. It pushes out temporary finger-like extensions called pseudopodia, which surround the food particle and fuse over it, enclosing it in a food vacuole. Enzymes inside the vacuole digest it, the useful products pass into the cytoplasm, and the residue is thrown out when the vacuole meets the surface. Paramoecium does the same job differently, using cilia to sweep food to a fixed point on its surface.
Saprophytic — the organism secretes digestive juices onto dead and decaying matter and then absorbs the dissolved products. Bread mould, yeast, mushrooms and Rhizopus feed this way. The digestion happens outside the body, which is the defining feature, and it is why a patch of mould spreads across bread rather than swallowing it.
Parasitic — the organism takes its food from the body of another living organism, the host, usually without killing it immediately. Cuscuta, also called amarbel, is a plant parasite that has no chlorophyll and draws its food from the plant it climbs on. Ticks, lice, leeches, roundworm and the malarial parasite are animal examples.
Worked classification. Classify a mushroom, a leech, a mango tree and an Amoeba.
- Mushroom — saprophytic, since it lives on dead organic matter and digests outside itself
- Leech — parasitic, since it feeds on a living host
- Mango tree — autotrophic, since it photosynthesises
- Amoeba — holozoic, since it takes in whole food particles
The distinction most often blurred. Saprophytes and parasites both live on other organisms, but a saprophyte needs its source to be dead while a parasite needs it to be alive. So a fungus on a rotting log is a saprophyte; the same kind of fungus growing on a living tree and harming it is a parasite. The state of the food source decides the name, not the organism.
A boundary case that is genuinely interesting. Some plants are green and photosynthesise, and also trap insects — the pitcher plant is the syllabus example. It cannot get enough nitrogen from the soil where it grows, so it obtains that one nutrient from the insect while making its carbohydrate itself. An organism can be autotrophic for energy and heterotrophic for a particular nutrient, which is why classification schemes describe the usual case rather than an absolute rule.
What happens to food at each stage of the alimentary canal?
Follow the food from mouth to anus, and name the juice, the enzyme and what it acts on at each stage.
Mouth. Teeth chew the food into small pieces, increasing its surface area, and the tongue mixes it with saliva. Saliva contains the enzyme salivary amylase, which begins the digestion of starch into sugar. This is why a mouthful of rice or bread begins to taste slightly sweet if you hold it long enough — the amylase has already started work.
Oesophagus. No digestion happens here. The food is pushed down by peristalsis, rhythmic waves of muscular contraction in the wall of the canal.
Stomach. The gastric glands in its wall release three things:
- Hydrochloric acid, which makes the contents acidic. The acid kills many swallowed bacteria and creates the acidic medium the next enzyme needs
- Pepsin, a protein-digesting enzyme that works only in an acidic medium
- Mucus, which coats and protects the stomach's own lining from the acid it has just produced
The mucus is not a detail. Without it the acid and the protein-digesting enzyme would attack the stomach wall, which is itself made of protein. A question asking why the stomach is not digested by its own juices wants the mucus lining as the answer.
A muscular sphincter at the exit releases the food into the small intestine in small amounts rather than all at once.
Small intestine — the longest part of the canal, and where digestion is completed. It receives two secretions from outside itself:
- Bile from the liver, stored in the gall bladder. Bile contains no enzyme. It makes the medium alkaline, which the pancreatic enzymes require, and it emulsifies fats — breaking large fat globules into small droplets so that enzymes can act on a much larger surface
- Pancreatic juice from the pancreas, containing amylase for starch, trypsin for proteins, and lipase for emulsified fats
The walls of the small intestine then secrete intestinal juice, which completes the job. The final products are:
Absorption happens here too. The inner surface is covered in tiny finger-like projections called villi, richly supplied with blood vessels, which give a very large surface for absorbing the digested food into the blood.
Large intestine. No digestion. Its walls absorb water from the unabsorbed material, and the rest is stored and then expelled through the anus — a process called egestion.
Why the acid-then-alkali sequence exists. Pepsin needs an acidic medium and the pancreatic enzymes need an alkaline one, so the food must be neutralised on the way from the stomach to the small intestine. Bile does that neutralising, which is its second job alongside emulsification. A question asking for the role of bile expects both.
One comparison that is regularly asked. The small intestine is longer in herbivores than in carnivores, because plant food contains cellulose, which takes far longer to digest. The length of a gut is evidence about a diet, which is why it is used to identify what an unfamiliar animal eats.
Mouth. Teeth chew the food into small pieces, increasing its surface area, and the tongue mixes it with saliva. Saliva contains the enzyme salivary amylase, which begins the digestion of starch into sugar. This is why a mouthful of rice or bread begins to taste slightly sweet if you hold it long enough — the amylase has already started work.
Oesophagus. No digestion happens here. The food is pushed down by peristalsis, rhythmic waves of muscular contraction in the wall of the canal.
Stomach. The gastric glands in its wall release three things:
- Hydrochloric acid, which makes the contents acidic. The acid kills many swallowed bacteria and creates the acidic medium the next enzyme needs
- Pepsin, a protein-digesting enzyme that works only in an acidic medium
- Mucus, which coats and protects the stomach's own lining from the acid it has just produced
The mucus is not a detail. Without it the acid and the protein-digesting enzyme would attack the stomach wall, which is itself made of protein. A question asking why the stomach is not digested by its own juices wants the mucus lining as the answer.
A muscular sphincter at the exit releases the food into the small intestine in small amounts rather than all at once.
Small intestine — the longest part of the canal, and where digestion is completed. It receives two secretions from outside itself:
- Bile from the liver, stored in the gall bladder. Bile contains no enzyme. It makes the medium alkaline, which the pancreatic enzymes require, and it emulsifies fats — breaking large fat globules into small droplets so that enzymes can act on a much larger surface
- Pancreatic juice from the pancreas, containing amylase for starch, trypsin for proteins, and lipase for emulsified fats
The walls of the small intestine then secrete intestinal juice, which completes the job. The final products are:
Absorption happens here too. The inner surface is covered in tiny finger-like projections called villi, richly supplied with blood vessels, which give a very large surface for absorbing the digested food into the blood.
Large intestine. No digestion. Its walls absorb water from the unabsorbed material, and the rest is stored and then expelled through the anus — a process called egestion.
Why the acid-then-alkali sequence exists. Pepsin needs an acidic medium and the pancreatic enzymes need an alkaline one, so the food must be neutralised on the way from the stomach to the small intestine. Bile does that neutralising, which is its second job alongside emulsification. A question asking for the role of bile expects both.
One comparison that is regularly asked. The small intestine is longer in herbivores than in carnivores, because plant food contains cellulose, which takes far longer to digest. The length of a gut is evidence about a diet, which is why it is used to identify what an unfamiliar animal eats.
Exam tip
What layout keeps a nutrition answer complete?
Name the organ, the juice, the enzyme and the substance acted on — four items, in that order. Digestion questions are marked on those details rather than on the narrative.
- Write the photosynthesis equation balanced, with sunlight and chlorophyll above the arrow and never among the reactants
- Say that the oxygen comes from the splitting of water, not from carbon dioxide
- Name both jobs of bile: it makes the medium alkaline and it emulsifies fats. Also say that it contains no enzyme
- Match each enzyme to its substrate: amylase to starch, pepsin and trypsin to proteins, lipase to fats
- State the medium each enzyme needs: pepsin acidic, pancreatic enzymes alkaline
- Explain the villi by surface area, and mention their blood supply
- For the nutrition types, give a named example each — Amoeba for holozoic, Rhizopus for saprophytic, Cuscuta for parasitic
- Describe guard cells as swelling and shrinking, and say that closing them limits water loss
The distinction to state carefully. Digestion and absorption are different steps: digestion breaks the food down, absorption moves it into the blood. The small intestine does both, and the large intestine does neither — it absorbs water only. A question about where digestion is completed and one about where water is absorbed have different answers, and confusing them is the commonest error in this chapter.
- Write the photosynthesis equation balanced, with sunlight and chlorophyll above the arrow and never among the reactants
- Say that the oxygen comes from the splitting of water, not from carbon dioxide
- Name both jobs of bile: it makes the medium alkaline and it emulsifies fats. Also say that it contains no enzyme
- Match each enzyme to its substrate: amylase to starch, pepsin and trypsin to proteins, lipase to fats
- State the medium each enzyme needs: pepsin acidic, pancreatic enzymes alkaline
- Explain the villi by surface area, and mention their blood supply
- For the nutrition types, give a named example each — Amoeba for holozoic, Rhizopus for saprophytic, Cuscuta for parasitic
- Describe guard cells as swelling and shrinking, and say that closing them limits water loss
The distinction to state carefully. Digestion and absorption are different steps: digestion breaks the food down, absorption moves it into the blood. The small intestine does both, and the large intestine does neither — it absorbs water only. A question about where digestion is completed and one about where water is absorbed have different answers, and confusing them is the commonest error in this chapter.
Did you know
Why can you swallow while standing on your head?
Food does not fall down your throat. If it did, swallowing while lying down would be impossible and drinking upside down would be a disaster.
What actually moves the food is peristalsis — a wave of muscular contraction that travels along the wall of the alimentary canal, squeezing just behind the food and relaxing just ahead of it. The food is pushed, not dropped, and the push works in any direction gravity happens to be pointing.
So the whole canal is a muscular conveyor belt, and that design has several consequences worth noticing.
- An animal can eat with its head below its stomach — which is how a grazing cow, a drinking dog and a giraffe reaching down to a pool all manage
- Astronauts in orbit eat and digest normally, because none of it depended on weight in the first place
- Peristalsis is why food keeps moving even through the long, coiled small intestine, where gravity could not help at all
The same muscular action explains a much less pleasant experience. Reverse the direction of the waves and the contents come back up. Vomiting is peristalsis running backwards, which is why it can happen whatever position the body is in.
And it explains why eating too fast causes trouble. The waves move at their own pace and the sphincters open only when the material ahead has moved on. Swallowing faster than the canal can push does not speed anything up — it only fills the oesophagus, which is what the uncomfortable feeling is.
The broader point is worth keeping. Almost every transport process in a large body is active rather than passive: food is pushed by muscles, blood is pumped by the heart, and water in a plant is pulled up by transpiration. Gravity is unreliable and one-directional, so living bodies do not depend on it — a design decision you will see again in every remaining part of this chapter.
What actually moves the food is peristalsis — a wave of muscular contraction that travels along the wall of the alimentary canal, squeezing just behind the food and relaxing just ahead of it. The food is pushed, not dropped, and the push works in any direction gravity happens to be pointing.
So the whole canal is a muscular conveyor belt, and that design has several consequences worth noticing.
- An animal can eat with its head below its stomach — which is how a grazing cow, a drinking dog and a giraffe reaching down to a pool all manage
- Astronauts in orbit eat and digest normally, because none of it depended on weight in the first place
- Peristalsis is why food keeps moving even through the long, coiled small intestine, where gravity could not help at all
The same muscular action explains a much less pleasant experience. Reverse the direction of the waves and the contents come back up. Vomiting is peristalsis running backwards, which is why it can happen whatever position the body is in.
And it explains why eating too fast causes trouble. The waves move at their own pace and the sphincters open only when the material ahead has moved on. Swallowing faster than the canal can push does not speed anything up — it only fills the oesophagus, which is what the uncomfortable feeling is.
The broader point is worth keeping. Almost every transport process in a large body is active rather than passive: food is pushed by muscles, blood is pumped by the heart, and water in a plant is pulled up by transpiration. Gravity is unreliable and one-directional, so living bodies do not depend on it — a design decision you will see again in every remaining part of this chapter.
Exam relevance
Why does NEET keep returning to photosynthesis and digestion?
This is foundation work for two of the largest Class 11 Biology chapters, both heavily examined in NEET.
Where photosynthesis leads. Class 11 Photosynthesis in Higher Plants takes the three steps you learn here and expands them into the light reaction and the Calvin cycle, with photosystems, the electron transport chain and the products ATP and NADPH named individually. The single fact that the oxygen comes from the splitting of water is examined directly — NEET sets it as a recall question, and it is the point most often misremembered.
Where stomata lead. Guard cells and their opening mechanism return in Class 11 Transport in Plants and Plant Growth, where the water potential of the guard cell is the explanation, and in the discussion of transpiration. The trade-off you meet here — carbon dioxide in against water out — is the whole reason those chapters exist.
Where digestion leads. Class 11 Digestion and Absorption repeats this alimentary canal with far more detail: named regions of the stomach, the enzymes in their inactive forms, the specific villi and microvilli, and the absorption route of each nutrient. Every enzyme you name here appears there, so the enzyme-to-substrate matching is worth learning exactly.
Where the bile answer leads. Emulsification is a NEET favourite, and the full answer is the two-ended-molecule mechanism from the soap chapter. A candidate who has met micelles in chemistry gives a better biology answer than one who has only memorised the word.
Question types to expect. At this level: write the equation, describe the steps, classify the nutrition, name the enzyme. In competitive papers: match-the-column for enzyme against substrate against site, assertion-reason items on the role of bile or of mucus, and diagram-based questions on the digestive system.
The single trap that costs marks. Writing sunlight or chlorophyll as a reactant in the photosynthesis equation. Both belong above the arrow: sunlight is energy, not matter, and chlorophyll is not consumed. An unbalanced equation is the second version of the same error.
A second trap. Saying that bile digests fat. Bile contains no enzyme — it emulsifies the fat and alkalises the medium so that lipase can digest it. In NEET this appears as an assertion-reason item and the distinction is the whole question.
Board versus competitive emphasis. The CBSE paper marks the equation, the named enzyme and the labelled diagram; a competitive paper marks a matched pair or a single fact. The transferable habit is naming the site, the secretion, the enzyme and the substrate together — four items that answer almost any digestion question.
Where photosynthesis leads. Class 11 Photosynthesis in Higher Plants takes the three steps you learn here and expands them into the light reaction and the Calvin cycle, with photosystems, the electron transport chain and the products ATP and NADPH named individually. The single fact that the oxygen comes from the splitting of water is examined directly — NEET sets it as a recall question, and it is the point most often misremembered.
Where stomata lead. Guard cells and their opening mechanism return in Class 11 Transport in Plants and Plant Growth, where the water potential of the guard cell is the explanation, and in the discussion of transpiration. The trade-off you meet here — carbon dioxide in against water out — is the whole reason those chapters exist.
Where digestion leads. Class 11 Digestion and Absorption repeats this alimentary canal with far more detail: named regions of the stomach, the enzymes in their inactive forms, the specific villi and microvilli, and the absorption route of each nutrient. Every enzyme you name here appears there, so the enzyme-to-substrate matching is worth learning exactly.
Where the bile answer leads. Emulsification is a NEET favourite, and the full answer is the two-ended-molecule mechanism from the soap chapter. A candidate who has met micelles in chemistry gives a better biology answer than one who has only memorised the word.
Question types to expect. At this level: write the equation, describe the steps, classify the nutrition, name the enzyme. In competitive papers: match-the-column for enzyme against substrate against site, assertion-reason items on the role of bile or of mucus, and diagram-based questions on the digestive system.
The single trap that costs marks. Writing sunlight or chlorophyll as a reactant in the photosynthesis equation. Both belong above the arrow: sunlight is energy, not matter, and chlorophyll is not consumed. An unbalanced equation is the second version of the same error.
A second trap. Saying that bile digests fat. Bile contains no enzyme — it emulsifies the fat and alkalises the medium so that lipase can digest it. In NEET this appears as an assertion-reason item and the distinction is the whole question.
Board versus competitive emphasis. The CBSE paper marks the equation, the named enzyme and the labelled diagram; a competitive paper marks a matched pair or a single fact. The transferable habit is naming the site, the secretion, the enzyme and the substrate together — four items that answer almost any digestion question.
Key takeaways
What should you know about nutrition before respiration?
One reason the processes never stop, one equation, four nutrition types and one canal.
- Life processes continue at rest because molecular structures constantly break down and must be rebuilt
- Single-celled organisms exchange everything across their whole surface; large bodies need organs and transport systems
- Photosynthesis: , with sunlight and chlorophyll above the arrow
- Three steps: light absorbed by chlorophyll, light energy converted and water split, carbon dioxide reduced to carbohydrate — and the oxygen comes from the water
- Stomata are bounded by guard cells that swell to open and shrink to close, balancing carbon dioxide intake against water loss
- Autotrophic — makes its own food; holozoic — takes in whole food, as Amoeba does with pseudopodia; saprophytic — digests dead matter outside the body, as Rhizopus does; parasitic — feeds on a living host, as Cuscuta does
- Mouth: salivary amylase on starch. Stomach: hydrochloric acid, pepsin on protein, mucus to protect the lining
- Small intestine: bile alkalises and emulsifies but contains no enzyme; pancreatic amylase, trypsin and lipase complete digestion; villi absorb
- Large intestine absorbs water only
- Herbivores have a longer small intestine than carnivores, because cellulose takes longer to digest
The sharpest self-test is the enzyme table. Write out the four stages of the canal from memory with the juice, the enzyme, the substrate and the product at each — and check whether you gave bile both of its jobs.
- Life processes continue at rest because molecular structures constantly break down and must be rebuilt
- Single-celled organisms exchange everything across their whole surface; large bodies need organs and transport systems
- Photosynthesis: , with sunlight and chlorophyll above the arrow
- Three steps: light absorbed by chlorophyll, light energy converted and water split, carbon dioxide reduced to carbohydrate — and the oxygen comes from the water
- Stomata are bounded by guard cells that swell to open and shrink to close, balancing carbon dioxide intake against water loss
- Autotrophic — makes its own food; holozoic — takes in whole food, as Amoeba does with pseudopodia; saprophytic — digests dead matter outside the body, as Rhizopus does; parasitic — feeds on a living host, as Cuscuta does
- Mouth: salivary amylase on starch. Stomach: hydrochloric acid, pepsin on protein, mucus to protect the lining
- Small intestine: bile alkalises and emulsifies but contains no enzyme; pancreatic amylase, trypsin and lipase complete digestion; villi absorb
- Large intestine absorbs water only
- Herbivores have a longer small intestine than carnivores, because cellulose takes longer to digest
The sharpest self-test is the enzyme table. Write out the four stages of the canal from memory with the juice, the enzyme, the substrate and the product at each — and check whether you gave bile both of its jobs.