Organs, digestion and enzymes
By the end of this chapter you will be able to
- Put cells, tissues, organs and organ systems in order, and name examples
- Name the organs of the digestive system and say what each one does
- Explain mechanical and chemical digestion, and name the enzymes that digest starch, protein and fat
- Use the lock-and-key model to explain how enzymes work, and read a temperature or pH graph
- Explain osmosis and active transport, and say when each one is needed
You should already know
- Cells, tissues and organs (Year 7 Chapter 2 and 3)
- Diffusion and particles (Year 7 Chapter 5)
Where this leads
- Respiration, which supplies the energy for active transport (Chapter 3)
National Curriculum for England, Key Stage 3 science, Year 8. Content: 8B1 cells are organised into tissues, organs and organ systems (briefly), 8B2 the human digestive system: its organs, mechanical and chemical digestion, enzymes as biological catalysts with lock-and-key action, and the effects of temperature and pH, 8B3 movement of substances into and out of cells: diffusion revisited, osmosis, and active transport.
Exercise P Do you remember?
Method. Recall the word.
- Recall. The basic unit of life is the cell.cell
- Write the answer. cell
Check. Cells are seen with a microscope. ✓
Method. Recall the sugar.
- Recall. Cells use glucose as their main energy source.glucose
- Write the answer. glucose
Check. Glucose is made by photosynthesis. ✓
Method. Find one quarter, then multiply by 3.
- One quarter. One quarter of 20 is 20 divided by 4, which is 5.20 / 4 = 5
- Three quarters. Three quarters is 3 times 5, which is 15.3 x 5 = 15
- Write the answer. 15
Check. 15 + 5 = 20, so 15 is three quarters of 20. ✓
Method. Recall the word.
- Recall. Movement from high to low concentration is diffusion.diffusion
- Write the answer. diffusion
Check. Particles spread out by diffusion. ✓
Method. Recall the word.
- Recall. A substance that dissolves is soluble.soluble
- Write the answer. soluble
Check. Sugar is soluble. ✓
Cells, tissues, organs and organ systems
Cells of the same type that work together form a tissue. Different tissues that work together for one job form an organ. Organs that work together for a body job form an organ system. The digestive system is one example.
The stomach wall is an organ made of several tissues. Its muscle tissue churns the food. Its glandular tissue makes digestive juices.
Key ideas
- A tissue is a group of similar cells working together.
- An organ is made of different tissues working together for one job.
- An organ system is a group of organs working together.
- Order from smallest to largest: cell, tissue, organ, organ system.
Method. Recall the level of organisation.
- Think. Similar cells, working together, form the next level up from a cell.similar cells
- Name it. That level is a tissue.tissue
- Write the answer. tissue
Check. Muscle is one example of a tissue. ✓
Method. Find the system for digestion.
- Look. The stomach, liver and mouth all take part in breaking down food.breaking down food
- Name it. Organs that work together to digest food form the digestive system.digestive system
- Write the answer. digestive system
Check. These are all organs of the digestive system. ✓
Method. Think about what churns.
- Think. Churning needs a tissue that can contract and squeeze.contract
- Name it. The muscle tissue of the stomach wall churns the food.muscle tissue
- Write the answer. muscle tissue
Check. The stomach wall has several tissues. ✓
Watch out
Watch out: a single cell is not a tissue. A tissue needs many similar cells working together.
Exam tip
Exam tip. Name the level in order: cell, tissue, organ, organ system, organism.
Try it (with your teacher, or a grown-up at home). Look at a labelled picture of a leaf or a cheek cell, and name each level: cell, tissue, organ. Say which level is the largest. Do not cut any living tissue yourself.
Exercise 2A Cells, tissues, organs and organ systems
Method. Recall the word.
- Recall. A group of similar cells working together is a tissue.tissue
- Write the answer. tissue
Check. Each tissue has one main job. ✓
Method. Recall the word.
- Recall. Different tissues working together for one job form an organ.organ
- Write the answer. organ
Check. The heart and the stomach are organs. ✓
Method. Recall the words.
- Recall. A group of organs working together for a body job is an organ system.organ system
- Write the answer. organ system
Check. The digestive system is one example. ✓
Method. Compare the levels.
- Compare. An organ is made of several tissues, so it is at a higher level.several tissues
- Decide. So an organ is the larger one.organ
- Write the answer. organ
Check. Cell, tissue, organ, organ system. ✓
Method. Find the system.
- Find it. These three organs all help to digest food.digest food
- Name it. The organ system is the digestive system.digestive system
- Write the answer. digestive system
Check. The liver makes bile. ✓
Method. Recall the organ.
- Recall. The liver makes bile, which helps to digest fat.liver
- Write the answer. liver
Check. Bile is stored in the gall bladder. ✓
Method. Recall the tissue.
- Recall. Muscle tissue can contract, so it churns the food.contract
- Write the answer. muscle tissue
Check. Muscle tissue is a tissue, not an organ. ✓
Method. Check the level.
- Check. The heart is made of several tissues working together for one job.several tissues
- Decide. So the heart is an organ, and the answer is yes.yes
- Write the answer. yes
Check. The heart pumps blood. ✓
Method. Check the number of cells.
- Check. A tissue needs many similar cells working together.many cells
- Decide. One cell is not a tissue, so the answer is no.no
- Write the answer. no
Check. Many muscle cells together make muscle tissue. ✓
Method. Recall the system.
- Recall. The heart, blood vessels and blood form the circulatory system.circulatory system
- Write the answer. circulatory system
Check. The heart is part of this system. ✓
Method. Use the order of organisation.
- Order. A cell is the smallest; a tissue is made of cells; an organ is made of tissues.cell, tissue, organ
- Write the answer. cell, tissue, organ
Check. Cell, tissue, organ, organ system. ✓
Method. Check the level.
- Check. The stomach is made of several tissues, including muscle, so it is an organ.several tissues
- Decide. So Ali is not right; the answer is no.no
- Write the answer. no
Check. Muscle is one tissue of the stomach. ✓
Method. Put the levels in order.
- Order. The first three levels are cell, tissue and organ.cell, tissue, organ
- Write the answer. cell, tissue, organ
Check. Organ systems come next. ✓
Method. Think about the tissues.
- Think. Each tissue does one part of the job.one part
- Conclude. Together the tissues carry out a larger job than one tissue can.larger job
- Write the answer. Accept any sentence that says an organ combines different tissues, each with its own job, so the organ can do a larger, more complex job.
Check. Teamwork between tissues makes the organ work. ✓
The digestive system
Digestion is the breaking down of large, insoluble food molecules into small, soluble ones. It has two kinds:
- Mechanical digestion breaks food into smaller pieces without changing the chemicals. Teeth chewing and the stomach churning are examples.
- Chemical digestion uses enzymes to change large molecules into smaller ones.
The table gives the main job of each organ.
| Organ | Main job |
|---|---|
| mouth | teeth chew food; saliva starts starch digestion |
| oesophagus | a muscular tube that moves food to the stomach |
| stomach | churns food; makes acid and the enzyme pepsin |
| liver | makes bile, which helps digest fat |
| pancreas | makes amylase, protease and lipase |
| small intestine | completes digestion and absorbs most food |
| large intestine | absorbs water from the remaining food |
Key ideas
- Digestion breaks large insoluble molecules into small soluble ones.
- Mechanical digestion breaks food into smaller pieces; chemical digestion uses enzymes.
- Most absorption happens in the small intestine.
- The large intestine absorbs water from the remaining food.
Method. Find the organ that absorbs food.
- Look. Most absorption happens in the long, folded lining of this organ.folded lining
- Name it. The small intestine absorbs most of the digested food.small intestine
- Write the answer. small intestine
Check. The large intestine absorbs water. ✓
Method. Decide whether the chemicals change.
- Think. Chewing makes the food smaller, but the chemicals stay the same.stay the same
- Name it. Breaking food into smaller pieces without changing it chemically is mechanical digestion.mechanical
- Write the answer. mechanical
Check. Enzymes make chemical digestion. ✓
Method. Recall the organ that makes acid.
- Recall. The stomach makes hydrochloric acid and pepsin.stomach
- Name it. So the organ is the stomach.stomach
- Write the answer. stomach
Check. The stomach contents are acidic. ✓
Watch out
Watch out: the pancreas and the liver are not part of the tube of food. They make substances that are poured into it.
Exam tip
Exam tip. Name the organ and its job. For example, “the stomach churns food and makes acid”.
Try it (with your teacher, or a grown-up at home). Look at the digestive system picture and trace the path of a piece of bread from the mouth to the large intestine. At each organ say whether digestion is mechanical, chemical, or absorption.
Exercise 2B The digestive system
Method. Recall the organ.
- Recall. The stomach churns and mixes food with acid.churns
- Write the answer. stomach
Check. Churning is mechanical digestion. ✓
Method. Recall the organ.
- Recall. Bile made by the liver is stored in the gall bladder.gall bladder
- Write the answer. gall bladder
Check. The gall bladder releases bile into the small intestine. ✓
Method. Recall the organ.
- Recall. The large intestine absorbs water from the food that remains.large intestine
- Write the answer. large intestine
Check. Remaining waste passes out of the body. ✓
Method. Recall the organ.
- Recall. The pancreas makes amylase, protease and lipase.pancreas
- Write the answer. pancreas
Check. These enzymes are released into the small intestine. ✓
Method. Think about the effect.
- Think. Mechanical digestion breaks food into smaller pieces.smaller pieces
- Decide. So it makes the food smaller.smaller
- Write the answer. smaller
Check. The chemicals stay the same. ✓
Method. Recall the enzyme.
- Recall. Amylase breaks down starch into sugars.amylase
- Write the answer. amylase
Check. Starch is a large carbohydrate. ✓
Method. Recall the enzyme.
- Recall. Protease breaks down proteins into amino acids.protease
- Write the answer. protease
Check. Protease is one type of enzyme. ✓
Method. Recall the enzyme.
- Recall. Lipase breaks down fats.lipase
- Write the answer. lipase
Check. Bile helps lipase work on fat. ✓
Method. Check whether the chemicals change.
- Check. Chewing breaks food into smaller pieces, but does not change its chemicals.does not change
- Decide. So chewing is mechanical digestion, and Ruby is not right; the answer is no.no
- Write the answer. no
Check. Enzymes make chemical digestion. ✓
Method. Recall the stomach contents.
- Recall. The stomach makes acid, so its contents are acidic.acid
- Decide. The word for this is acidic.acidic
- Write the answer. acidic
Check. Acid makes the stomach contents acidic. ✓
Method. Follow the path of food.
- Follow. Food passes from the oesophagus into the stomach, and is stored and churned there.stored
- Name it. So the organ is the stomach.stomach
- Write the answer. stomach
Check. The stomach stores food before it passes on. ✓
Method. Think about the size of food.
- Think. Large food molecules are too big to pass through the gut wall.too big
- Conclude. So digestion breaks them into small soluble molecules that can be absorbed.small soluble
- Write the answer. Accept any sentence that says large insoluble food molecules must be broken into small soluble ones before they can pass through the gut wall.
Check. Digestion makes absorption possible. ✓
Enzymes as biological catalysts
An enzyme is a protein that acts as a biological catalyst. A catalyst speeds up a reaction and is not used up. The molecule an enzyme acts on is the substrate. The enzyme has an active site with a specific shape, and the substrate fits into it. This is the lock-and-key model. The substrate is changed into products, and the enzyme is released unchanged.
The table gives the three main digestive enzymes.
| Enzyme | Substrate | Products |
|---|---|---|
| amylase | starch | sugars |
| protease | proteins | amino acids |
| lipase | fats | fatty acids and glycerol |
Key ideas
- Enzymes are proteins that act as biological catalysts.
- The substrate fits the active site of one specific enzyme.
- Enzymes are not used up, so a small amount can break down a lot of substrate.
- Each enzyme changes its own substrate into specific products.
Method. Recall the definition.
- Recall. The molecule an enzyme acts on is the substrate.substrate
- Check. The substrate is changed into products by the enzyme.changed into products
- Decide. So the name is substrate.substrate
- Write the answer. substrate
Check. The products are made from the substrate. ✓
Method. Recall the part of the enzyme.
- Recall. The substrate fits into the active site.active site
- Check. The active site has a specific shape that matches the substrate.specific shape
- Decide. So the part is the active site.active site
- Write the answer. active site
Check. The active site has a specific shape. ✓
Method. Recall what enzymes are made of.
- Recall. Enzymes are proteins.protein
- Decide. So an enzyme is a protein, not a sugar.protein
- Write the answer. protein
Check. Protein molecules have specific shapes. ✓
Watch out
Watch out: an enzyme is not used up in the reaction. It can be used again, and it is released unchanged.
Exam tip
Exam tip. Describe the lock-and-key model in one sentence: the substrate fits the active site of one specific enzyme.
Try it (with your teacher, or a grown-up at home). With a grown-up, chew a plain cracker slowly and notice when it starts to taste sweet. Say which enzyme you think is at work, and which substrate it acts on. Do not add any substance to your mouth or to anyone else’s.
Exercise 2C Enzymes as biological catalysts
Method. Recall what enzymes are.
- Recall. Enzymes are proteins.protein
- Write the answer. protein
Check. Enzymes have a shape that matters. ✓
Method. Recall the word.
- Recall. A catalyst speeds up a reaction and is not used up.catalyst
- Write the answer. catalyst
Check. Enzymes are biological catalysts. ✓
Method. Recall the word.
- Recall. The molecule an enzyme acts on is the substrate.substrate
- Write the answer. substrate
Check. The substrate is changed into products. ✓
Method. Recall the part.
- Recall. The active site is the part of the enzyme where the substrate fits.active site
- Write the answer. active site
Check. The active site has a specific shape. ✓
Method. Recall the model.
- Recall. The model in which a specific substrate fits a specific enzyme is lock and key.lock and key
- Write the answer. lock and key
Check. A key fits one lock. ✓
Method. Recall the definition.
- Recall. A catalyst is not used up in the reaction.not used up
- Decide. So the enzyme is not used up, and the answer is no.no
- Write the answer. no
Check. The enzyme is released unchanged. ✓
Method. Recall the products.
- Recall. Amylase breaks starch down into sugars.sugars
- Write the answer. sugars
Check. Starch is a large carbohydrate. ✓
Method. Recall the products.
- Recall. Protease breaks proteins into amino acids.amino acids
- Write the answer. amino acids
Check. Amino acids are small molecules. ✓
Method. Recall the products.
- Recall. Lipase breaks fats into fatty acids and glycerol.fatty acids and glycerol
- Write the answer. fatty acids and glycerol
Check. Two kinds of product. ✓
Method. Check the definition.
- Check. Enzymes are proteins that speed up reactions in living things.speed up
- Decide. So the statement is true, and the answer is yes.yes
- Write the answer. yes
Check. Biological means made by living things. ✓
Method. Check whether the enzyme is used up.
- Check. An enzyme is a catalyst, so it is released unchanged after the reaction.released unchanged
- Decide. So Ali is not right; the answer is no.no
- Write the answer. no
Check. The same enzyme can act again. ✓
Method. Use the lock-and-key model.
- Think. The substrate must fit the active site for the enzyme to work.must fit
- Conclude. If it does not fit, the reaction does not happen with this enzyme.not at all
- Write the answer. not at all
Check. Only the right enzyme works on a given substrate. ✓
Method. Think about the shape.
- Think. The active site has a specific shape.specific shape
- Conclude. So only one substrate fits and can be changed.only one substrate
- Write the answer. Accept any sentence that says the active site has a specific shape that only fits one substrate.
Check. Specific shape means specific substrate. ✓
Temperature and pH
Enzymes work fastest at a particular temperature, called the optimum. At low temperatures the molecules move slowly, so the reaction is slow. As the temperature rises, the enzyme and substrate collide more often, and the rate rises.
At high temperatures the enzyme's shape changes so that the active site no longer fits the substrate. The enzyme is denatured. Denaturing is not reversible. Each enzyme also has an optimum pH; a pH far from it slows the enzyme down.
The table gives class data for starch breakdown at six temperatures. The rate is worked out as 1000 divided by the time.
| Temperature (degrees C) | Time for the iodine to stop turning blue-black (s) | Rate (1000 / time) |
|---|---|---|
| 10 | 250 | 4 |
| 20 | 200 | 5 |
| 30 | 100 | 10 |
| 40 | 50 | 20 |
| 50 | 100 | 10 |
| 60 | 500 | 2 |
The table gives the optimum pH of two enzymes.
| Enzyme | Where it works | Optimum pH |
|---|---|---|
| pepsin | stomach | about 2 |
| salivary amylase | mouth | about 7 |
Key ideas
- Each enzyme works fastest at its optimum temperature.
- Above the optimum, the enzyme denatures and the rate falls.
- Denaturing is permanent: the active site loses its shape.
- Each enzyme has its own optimum pH.
Method. Find the largest rate.
- Read the rates. The rates are 4, 5, 10, 20, 10 and 2.highest is 20
- Name the temperature. The highest rate, 20, is at 40 degrees C.40
- Write the answer. 40 degrees C
Check. Rates above and below 40 are lower. ✓
Method. Find the row for 30 degrees.
- Read. At 30 degrees C the time is 100 seconds.100 s
- Calculate. The rate is 1000 divided by 100.1000 / 100 = 10
- Write the answer. 10
Check. 10 x 100 = 1000. ✓
Method. Find the optimum pH.
- Look. The optimum pH of pepsin is about 2, and it works in the stomach.about 2
- Name it. So the enzyme is pepsin.pepsin
- Write the answer. pepsin
Check. Salivary amylase works best at about pH 7. ✓
Watch out
Watch out: a high temperature does not make an enzyme work faster. Above the optimum, it denatures and the rate falls.
Exam tip
Exam tip. Say “denatured, the active site has changed shape, so the substrate no longer fits”.
Try it (with your teacher, or a grown-up at home). Ask your teacher to show the class the starch and iodine test, with a warm water bath and the same amount of starch and amylase in each tube. Note the time for the iodine to stop turning blue-black. Do not handle the hot water or the iodine yourself.
Exercise 2D Temperature and pH
Method. Recall the word.
- Recall. The temperature at which an enzyme works fastest is its optimum.optimum
- Write the answer. optimum
Check. Above the optimum, the enzyme denatures. ✓
Method. Recall the word.
- Recall. When an enzyme loses its shape, it is denatured.denatured
- Write the answer. denatured
Check. A denatured enzyme cannot bind the substrate. ✓
Method. Recall the fact.
- Recall. Once the active site has changed shape, it does not return.does not return
- Decide. So denaturing is not reversible, and the answer is no.no
- Write the answer. no
Check. A denatured enzyme must be replaced. ✓
Method. Read the row for 20 degrees.
- Read. The time at 20 degrees C is 200 seconds.200 s
- Calculate. The rate is 1000 divided by 200.1000 / 200 = 5
- Write the answer. 5
Check. 5 x 200 = 1000. ✓
Method. Find the shortest time.
- Look. The shortest time is 50 seconds.50 s
- Name it. That is at 40 degrees C.40
- Write the answer. 40
Check. The shortest time gives the highest rate. ✓
Method. Subtract the two rates.
- Subtract. The rate at 40 degrees C is 20, and at 50 degrees C it is 10.20 and 10
- Calculate. The difference is 20 minus 10.20 - 10 = 10
- Write the answer. 10
Check. 10 + 10 = 20. ✓
Method. Recall the enzyme.
- Recall. Pepsin works in the stomach, where the pH is low.stomach
- Write the answer. pepsin
Check. Pepsin is a protease. ✓
Method. Read the table.
- Read. The optimum pH of pepsin is about 2.about 2
- Write the answer. 2
Check. The stomach is strongly acidic. ✓
Method. Recall the effect.
- Recall. A pH far from the optimum changes the enzyme shape and slows the reaction.slows
- Write the answer. slows
Check. The rate falls away from the optimum. ✓
Method. Look at the rates.
- Look. At 60 degrees C the rate is 2, the lowest in the table.lowest
- Decide. So the enzyme works best near 40 degrees C; Ali is not right, and the answer is no.no
- Write the answer. no
Check. Read the rate column, not the temperature. ✓
Method. Multiply the temperatures by the repeats.
- Multiply. There are 6 temperatures, each repeated 3 times: 6 x 3.6 x 3
- Calculate. So 18 tests are carried out.6 x 3 = 18
- Write the answer. 18
Check. Repeats show the spread of the results. ✓
Method. Think about the enzyme.
- Think. pH affects enzyme activity as well as temperature.affects
- Conclude. So a change in pH would confuse the effect of temperature.confuse
- Write the answer. Accept any sentence that says a change in pH would change the enzyme activity too, so the effect of temperature could not be separated out.
Check. Keep all control variables the same. ✓
Osmosis and active transport
Diffusion is the net movement of particles from a high concentration to a low concentration, down a concentration gradient.
Osmosis is the diffusion of water through a partially permeable membrane, from a dilute solution (more water) to a concentrated solution (less water).
Active transport moves substances from a low concentration to a high concentration, against the concentration gradient. It needs energy from respiration. Plant root hair cells use it to absorb mineral ions from the soil.
The table gives the mass change of the potato cylinders after one hour.
| Sugar solution | Mass change (g) |
|---|---|
| 0%: pure water | +2.0 |
| 5% sugar | +0.5 |
| 10% sugar | -1.0 |
| 15% sugar | -2.5 |
Key ideas
- Diffusion: movement from high to low concentration down a gradient.
- Osmosis: movement of water through a partially permeable membrane, from dilute to concentrated.
- Active transport: movement against the gradient, using energy from respiration.
- Osmosis needs no energy; active transport does.
Method. Recall the direction of osmosis.
- Recall. Water moves from the solution with more water to the solution with less water.more water
- Decide. So water moves from dilute to concentrated.dilute to concentrated
- Write the answer. from dilute to concentrated
Check. The concentrated solution takes water in. ✓
Method. Find the largest positive mass change.
- Read. The largest gain is in the pure water, at +2.0 g.+2.0
- Name it. So the solution is pure water, 0%.0%: pure water
- Write the answer. 0%: pure water
Check. Pure water is the most dilute. ✓
Method. Recall the example.
- Recall. Root hair cells absorb mineral ions from the soil by active transport.mineral ions
- Name it. So an example is mineral ions.mineral ions
- Write the answer. Accept any one: mineral ions.
Check. Mineral ions are in low concentration in the soil water. ✓
Watch out
Watch out: osmosis is the movement of water only. It is a special case of diffusion, through a membrane that lets water through but not all particles.
Exam tip
Exam tip. State the direction: osmosis from dilute to concentrated; active transport against the gradient, with energy.
Try it (with your teacher, or a grown-up at home). Look at the mass change table. With your teacher, explain why the cylinder in 10 percent sugar lost mass. Do not cut any potato yourself unless your teacher asks you to.
Exercise 2E Osmosis and active transport
Method. Recall the word.
- Recall. Movement from high to low concentration is diffusion.diffusion
- Write the answer. diffusion
Check. Diffusion needs no energy. ✓
Method. Recall the word.
- Recall. The movement of water through a partially permeable membrane is osmosis.osmosis
- Write the answer. osmosis
Check. Only water moves in osmosis. ✓
Method. Recall the direction.
- Recall. Water moves from the dilute solution to the concentrated solution.dilute to concentrated
- Write the answer. dilute to concentrated
Check. Water moves towards less water. ✓
Method. Recall the definition.
- Recall. Active transport moves substances against the concentration gradient.against
- Write the answer. against the concentration gradient
Check. Diffusion goes down the gradient. ✓
Method. Recall the fact.
- Recall. Moving substances against the gradient needs energy.needs energy
- Decide. So the answer is yes.yes
- Write the answer. yes
Check. Diffusion does not need energy. ✓
Method. Recall the process.
- Recall. Cells release energy from glucose by respiration.respiration
- Write the answer. respiration
Check. Respiration releases energy in cells. ✓
Method. Recall the example.
- Recall. Root hair cells absorb mineral ions from the soil by active transport.mineral ions
- Write the answer. Accept any one: mineral ions.
Check. The ions are in low concentration in the soil water. ✓
Method. Read the row for pure water.
- Read. The mass change in pure water is +2.0 g.+2.0
- Write the answer. +2.0
Check. A gain is shown with a plus sign. ✓
Method. Find the most negative value.
- Look. The most negative value is -2.5 g, in 15 percent sugar.-2.5
- Name it. So the greatest loss is in 15% sugar.15%
- Write the answer. 15%
Check. Water moved out of the cylinder in the most concentrated solution. ✓
Method. Read the row for 5 percent sugar.
- Read. The mass change in 5% sugar is +0.5 g.+0.5
- Write the answer. +0.5
Check. A small gain. ✓
Method. Check the table.
- Check. In pure water the mass change is +2.0 g, a gain.+2.0 g
- Decide. So Ali is not right; the answer is no.no
- Write the answer. no
Check. Water moves into the cylinder in pure water. ✓
Method. Compare the two processes.
- Compare. Osmosis is the diffusion of water only, through a partially permeable membrane.water only
- Decide. Osmosis is a special case of diffusion, so Ruby is not right; the answer is no.no
- Write the answer. no
Check. Osmosis needs a membrane; diffusion does not. ✓
Method. Think about the gradient.
- Think. The mineral ions are at a higher concentration inside the root hair cell than outside.higher inside
- Conclude. Moving them in against the gradient needs energy from respiration.needs energy
- Write the answer. Accept any sentence that says the mineral ions move against the concentration gradient, so energy from respiration is needed.
Check. Diffusion alone could not do this. ✓
Chapter summary
| Skill | Method |
|---|---|
| Organisation | Cell, tissue, organ, organ system. Example: stomach wall tissues make up the stomach. |
| Digestion | Mechanical (chewing, churning) makes food smaller; chemical (enzymes) changes molecules. |
| Enzymes | Protein biological catalysts; lock-and-key active site; not used up. |
| Temperature and pH | Each enzyme has an optimum; above the optimum it denatures, which cannot be reversed. |
| Osmosis | Water moves through a partially permeable membrane from dilute to concentrated. |
| Active transport | Movement against the gradient, needing energy from respiration. |
Can you…?
- I can put cells, tissues, organs and organ systems in order
- I can name the organs of the digestive system and say what each does
- I can explain mechanical and chemical digestion, and name the three main enzymes
- I can use the lock-and-key model to explain how an enzyme works
- I can read a temperature or pH table, and explain denaturing
- I can explain osmosis and active transport, and say when each is needed
Key terms
- tissue
- a group of similar cells working together
- organ
- different tissues working together for one job
- digestion
- breaking down large insoluble food molecules into small soluble ones
- enzyme
- a protein that acts as a biological catalyst
- substrate
- the molecule an enzyme acts on
- active site
- the part of an enzyme where the substrate fits
- denatured
- an enzyme whose active site has changed shape, so it no longer works
- osmosis
- the movement of water through a partially permeable membrane, from dilute to concentrated
- active transport
- movement of substances against a concentration gradient, using energy from respiration
Exercise 2Z Check-up
Method. Recall the system.
- Recall. The stomach and the liver are both organs of the digestive system.digestive system
- Write the answer. digestive system
Check. The system digests food. ✓
Method. Recall the organ.
- Recall. The small intestine absorbs most of the digested food.small intestine
- Write the answer. small intestine
Check. The large intestine absorbs water. ✓
Method. Recall the enzyme.
- Recall. Amylase breaks down starch into sugars.amylase
- Write the answer. amylase
Check. Amylase is made in the mouth and the pancreas. ✓
Method. Recall the word.
- Recall. A catalyst speeds up a reaction and is not used up.catalyst
- Write the answer. catalyst
Check. Enzymes are biological catalysts. ✓
Method. Recall the part.
- Recall. The substrate fits into the active site.active site
- Write the answer. active site
Check. The active site has a specific shape. ✓
Method. Read the row and divide.
- Read. At 30 degrees C the time is 100 seconds.100 s
- Calculate. 1000 divided by 100 is 10.1000 / 100 = 10
- Write the answer. 10
Check. 10 x 100 = 1000. ✓
Method. Recall the word.
- Recall. The movement of water through a partially permeable membrane is osmosis.osmosis
- Write the answer. osmosis
Check. Water moves from dilute to concentrated. ✓
Method. Recall the process.
- Recall. Moving substances against the gradient, using energy, is active transport.active transport
- Write the answer. active transport
Check. Diffusion does not need energy. ✓
Method. Recall the enzyme.
- Recall. Pepsin works best in the stomach, at about pH 2.pepsin
- Write the answer. pepsin
Check. Pepsin is a protease. ✓
Method. Think about the shape.
- Think. High temperature changes the shape of the enzyme.changes shape
- Conclude. The substrate no longer fits, so the enzyme cannot work.no longer fits
- Write the answer. Accept any sentence that says the high temperature denatures the enzyme, so its active site changes shape and no longer fits the substrate.
Check. Denatured enzymes cannot be restored. ✓
Total 14 marks. Allow about 14 minutes.
Exercise 2X Practice test questions
Method. Recall the word.
- Recall. A group of similar cells working together is a tissue.tissue
- Write the answer. tissue
Check. The next level is an organ. ✓
Method. Recall the organ.
- Recall. The liver makes bile.liver
- Write the answer. liver
Check. Bile helps to break up fat. ✓
Method. Compare the two.
- Mechanical. Mechanical digestion breaks food into smaller pieces.smaller pieces
- Chemical. Chemical digestion uses enzymes to change the molecules.enzymes
- Write the answer. Accept any sentence that says mechanical digestion breaks food into smaller pieces without changing its chemicals, and chemical digestion uses enzymes to change the molecules.
Check. Chewing is mechanical; amylase is chemical. ✓
Method. Recall the enzyme.
- Recall. Lipase breaks down fats.lipase
- Write the answer. lipase
Check. Fats become fatty acids and glycerol. ✓
Method. Find the highest rate.
- Look. The highest rate in the list is 20.20
- Name it. The rate of 20 is at 40 degrees C.40
- Write the answer. 40
Check. 40 degrees C is the optimum for this data. ✓
Method. Think about the active site.
- Think. The active site loses its shape.loses its shape
- Conclude. The substrate can no longer fit, so the enzyme stops working.stops working
- Write the answer. Accept any sentence that says the active site changes shape so the substrate no longer fits, and this change cannot be reversed.
Check. Denaturing is permanent. ✓
Method. Recall the direction.
- Recall. Water moves from more water to less water, so from dilute to concentrated.dilute to concentrated
- Decide. So the statement is true, and the answer is yes.yes
- Write the answer. yes
Check. The direction follows the water concentration. ✓
Method. Recall the process.
- Recall. Movement against the gradient, using energy, is active transport.active transport
- Write the answer. active transport
Check. Diffusion goes down the gradient. ✓
Method. Find the small positive value.
- Look. The small gain is +0.5 g, in 5 percent sugar.+0.5
- Name it. So the solution is 5% sugar.5%
- Write the answer. 5%
Check. Only pure water and 5% sugar give a gain. ✓
Method. Think about the rate.
- Think. The amount of substrate can change the rate.change the rate
- Conclude. So it must be a control variable.control variable
- Write the answer. Accept any sentence that says a different amount of substrate would change the rate, so the effect of temperature could not be separated out.
Check. Keep control variables the same. ✓