What is a tissue?
A group of similar cells that work together to perform a specific function.
contracts to move what it's attached to.
makes and secretes chemicals like enzymes or hormones.
covers some parts of the body, e.g. the inside of the gut.
Explain what is meant by the term "organ system".
A group of organs working together to perform a specific function.
What does the digestive system do?
Breaks down and absorbs food.
What is the digestive system made up of?
Glands, e.g. the pancreas and salivary glands, which produce digestive juices.
The stomach, which digests food.
The small intestine, which digests food and absorbs soluble food molecules.
The liver, which produces bile.
The large intestine, which absorbs water from undigested food, leaving faeces.
Why can enzymes be described as biological catalysts?
They reduce the need for high temperatures (which can speed up unwanted reactions and harm cells) by speeding up reactions in the body.
What is a catalyst?
A substance which increases the speed of a reaction without being changed or used up in the reaction.
What are enzymes and what are they made out of?
They are large proteins and all proteins are made of chains of amino acids. They are folded into unique shapes, which enzymes need to have their different active sites.
The substance that an enzyme acts on is called the...
Why do enzymes usually only catalyse one reaction?
For enzymes to work, the substrate has to fit into its active site. If it doesn't, the reaction won't be catalysed.
Why is the lock and key model of enzymes slightly inaccurate?
In reality, the active site changes shape a little as the substrate binds to it, to get a tighter fit. This is the induced fit model of enzyme action.
What is meant by an enzyme being "denatured"?
An increase in temperature will first increase the rate of reaction. However, at a certain temperature, bonds in an enzyme can be broken. This changes the shape of the active site- so the substrate doesn't fit.
The enzyme amylase catalyses the breakdown of starch to maltose. Iodine can be used to detect starch- if starch is present, iodine solution will change from browny-orange to blue-black.
Describe how you could investigate the effect of pH on the rate of amylase activity.
1) Put a drop of iodine solution into every well of a spotting tile.
2) Place a bunsen burner on a heatproof mat and a tripod and gauze over the bunsen burner.
3) Put a beaker of water on top of the gauze and heat it until it reacher 35°C (measure using a thermometer). Try to keep the water temperature constant throughout the experiment.
4)Put a boiling tube in the beaker. Use a syringe to add 1cm3 of amylase solution and 1cm3 of a buffer solution (pH 5) to the boiling tube.
5) Use a different syringe to add 5cm3 of a starch solution to the boiling tube. Immediately mix the contents and start a stopwatch.
6) Use continuous sampling to record how long it takes for the amylase to break down all of the starch. Do this by using a pipette to take a sample from the boiling tube every 30 seconds and putting a drop into different wells of the spotting tile. When the iodine solution remains browny-orange, starch is no longer present.
7) Repeat the experiment with buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken down.
The enzymes used in digestion are produced by ___ and then released into the ___ to mix with food.
specialised cells in glands and in the gut lining, gut.
What do enzymes do to starch, proteins and fats, and why?
They are molecules too big to pass through the walls of the digestive system- they can't be absorbed into the bloodstream. Enzymes break them down into smaller, soluble molecules.
Give 4 examples of smaller molecules that result from enzymes breaking down starches, proteins and fats.
Sugars (e.g. glucose and maltose), amino acids, glycerol and fatty acids.
Starch is a....
In what three places is amylase made?
- The salivary glands
- The pancreas
- The small intestine
What is amylase and what does it do?
It is a carbohydrase and it catalyses the breakdown of starch- a carbohydrate- into maltose and other sugars like dextrins.
What do proteases do?
Convert proteins into amino acids.
In what three places are proteases made?
- The stomach (it's called pepsin there)
- The pancreas
- The small intestine
What do lipases do?
Convert lipids into glycerol and fatty acids.
In what two places are lipases made?
- The pancreas
- The small intestine
What does the body do with the products of digestion?
- Make them into new carbohydrates, proteins and lipids
- Some glucose is used in respiration
Where is bile produced?
In the liver.
Where is bile stored before it's released into the small intestine?
The gall bladder.
What does bile do?
Neutralises stomach acid: hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly. Bile is alkaline so it neutralises the acid and makes conditions alkaline, which is best for enzymes in the small intestine.
- Emulsifies fats: breaks fats into tiny droplets, giving fats a bigger surface area for the enzyme lipase to work on. This makes its digestion faster.
An enzyme controlled reaction was carried out at pH 4. After 60 seconds, 33cm3 of product had been released. Calculate the rate of reaction in cm3 s-1.
33/60 = 0.55cm3 s-1
What is the formula used to calculate the rate of reaction for a certain pH?
Amount of product formed = change
change/time(s) = s-1 (2 s.f.)
(cm3 s-1 is another way of writing cm3/s)
How is a leaf's structure adapted so that carbon dioxide can diffuse into cells for photosynthesis?
- The underneath of the leaf is an exchange surface, covered in holes, called stomata, which the carbon dioxide diffuses in through
- Oxygen (produced in photosynthesis) and water vapour diffuse out of the stomata
- The size of stomata are controlled by guard cells, which close them if the plant is losing water faster than it is being replaced by the roots
- The flattened shape of the leaf increases the area of the exchange surface so that diffusion happens faster
- The walls of the cells in the leaf form another exchange surface- air between them increase the surface area so carbon dioxide can diffuse into cells faster
Give 5 examples of plant tissues and where they are found.
1) Epidermal tissue: covers the whole plant.
2) Palisade mesophyll tissue: close to the surface of the leaf.
3) Spongy mesophyll tissue: in the middle of the leaf.
4) Xylem and phloem: transport things like water, mineral ions and food around the plant.
5) Meristem tissue: found at the growing tips of shoots and roots. Is able to differentiate into many different types of plant cell, allowing growth.
How is the structure of epidermal tissue related to its function?
It is covered with a waxy cuticle which helps to reduce water lost by evaporation.
How is the structure of the upper epidermis related to its function?
It is transparent so that light can pass through to the palisade layer.
How is the structure of the palisade layer releated to its function?
It is near the top of the leaf where it can get the most light. It has lots of chloroplasts; most photosynthesis happens here.
How is the structure of xylem and phloem tissue releated to its function?
These cells form a network of vascular bundles which deliver water and other nutrients to the entire leaf, and take away the glucose produced by photosynthesis. They also help support the leaf's structure.
How is the structure of spongy mesophyll tissue releated to its function?
There are many air spaces, which increase the rate of diffusion of gases.
How is the structure of the lower epidermis releated to its function?
The underneath of the leaf is an exchange surface, covered in holes, called stomata, which the carbon dioxide diffuses in through, and oxygen (produced in photosynthesis) and water vapour diffuse out through.
The size of stomata are controlled by guard cells, which open and close stomata in response to environmental conditions. Stomata are closed if the plant is losing water faster than it is being replaced by the roots. This prevents the plant wilting.
transport food substances (mainly dissolved sugars), made in the leaves, to the rest of the plant for immediate use (like growth) or for storage.
Transport goes in both directions.
carry water and mineral ions from the roots to the stem and leaves. Xylem tubes only transport things upwards.
What are phloem tubes made of?
Elongated living cells with small pores in the end walls to allow cell sap to flow through.
What is the process of phloem tubes transporting food called?
The movement of water from the roots, through the xylem tubes and out of the leaves is called...
The transpiration stream.
Most transpiration happens...
at the leaves.
Transpiration is caused by the ___ and ___ of water from a plant's surface.
Why is there a constant transpiration stream of water through plants?
Leaves have to have stomata for gas exchange in photosynthesis. This however means that water diffuses through the stomata, so it has to be soaked up again from the roots. This creates the stream.
What are the 4 main things that affect transpiration rate?
1) Light intensity: the brighter the light, the greater the transpiration rate (photosynthesis can't happen in the dark so stomata won't be open).
2) Temperature: the warmer it is, the greater the transpiration rate (diffusion happens more).
3) Air flow: the more air flow (wind) around a plant, the greater the transpiration rate (water vapour is blown away, maintaining a high concentration gradient for diffusion).
4) Humidity: the drier the air, the greater the transpiration rate (concentration gradient again).
How can the rate of transpiration be measured?
Measuring the uptake of water by a plant (because you can assume this is directly related to water loss). This can be recorded with a potometer.
How are guard cells adapted to open and close stomata (and therefore gas exchange and controlling water loss)?
- Kidney shape, with the stoma (singular) in the middle
- When the plant has a lot of water, the guard cell becomes turgid, opening the stoma for photosynthesis
- When the plant is short of water, the guard cell becomes flaccid, closing the stoma to limit water loss
- Thin outer walls and thickened inner walls to make the opening and closing work
- Sensitive to light- they close at night to save water
- More guard cells on the underside, which is cool and shaded, reducing the transpiration rate
What is transpiration (not transpiration stream)?
The loss of water from plants.