Cell Organisation
- Cells are the basic building blocks that make up all living organisms. Specialised cells carry out a particular function.
- Specialised cells are formed by a process called differentiation. This occurs during development of a multicellular organism/
- These specialised cells form tissues, which form organs, which form organ systems, which form large multicellular organisms, such as humans.
The systems inside these organisms are used for exchanging and transporting materials.
Tissues
- Tissues are a group of similar cells that group to carry out a particular function. These can include more than one type of cell. In mammals:
Organs
- An organ is a group of tissues that work together to perform a certain function.
- The stomach is made up of Muscular tissue,
Glandular tissue and Epithelial tissue.
Organ Systems
- An organ system is a group of organs working together to perform a particular
function.
- Organ systems work together to form large multicellular organisms/organisms.
Enzymes
- Living things have thousands of chemical reactions going on inside them all the time,
and these reactions need to be carefully controlled, to get the right amount of
substances.
- You can usually make a reaction happen faster by raising the temperature, but
unfortunately this makes all the reactions speed up, the useful ones and the unwanted
ones. There is also a limit to how high you can raise the temperature before cells start getting damaged.
- To solve this, living things produce enzymes, biological catalysts. Enzymes reduce the need for high temperature, and only work on their
specific reaction.
- Catalysts lower the activation energy needed to perform a chemical reaction, and this means less energy and time go into these reactions.
- Enzymes are large proteins, which are made by chains of amino acids, which are folded into unique shapes, so only work on specific reactions.
- Every enzyme has an active site with a unique shape that fits only onto the substance involved in the reaction.
- This means enzymes only work for one specific reaction.
- This is because, for the enzyme to work, the substrate has to fit into the active site. If it doesn't, the reaction won't be catalysed- “Lock and Key
model”.
, - This is simpler than how they
actually work, in reality the
active site changes shape a little
as the substrate binds to it to
get a tighter fit - the ‘induced fit’
model of enzyme action.
- Changing the temperature also changes the rate of an enzyme reaction.
- Increase in temperature results in increase in rate. If the temperature gets too high, the enzyme
could denature after some of the bonds holding the enzyme together break. With the enzyme being
denatured, the substrate for the enzyme may not fit so the reaction will not be catalysed.
- All enzymes have an optimum temperature.
- The optimum temperature for most is around the same temperature as the human body, about
37C.
- The pH also affects temperature, for the same reasons as before- it could be denatured.
- Most work at neutral pH 7, but some enzymes, such as pepsin, which breaks down proteins in the
stomach, works best at pH 2. This makes it well suited to the acidic conditions in the stomach.
Investigating the Effect of pH on Enzyme Activity
The enzyme amylase catalyses the breakdown of starch to maltose. It is easy to detect starch using
iodine solution- if starch is present, the iodine solution will change from
brown/orange to blue/black. This is how you can investigate how pH affects
amylase activity.
1. Put a drop of iodine solution into every well of a spotting tile.
2. Place a beaker of water over a Bunsen burner, on top of a tripod. Heat the
water until it is 35C, using a thermometer to measure this. Try to keep the
temperature of the water constant throughout the experiment.
3. Use a syringe to add 1cm3 of amylase solution and 1 cm3 of a buffer solution
with a pH of 5 to a boiling tube. Using test tube holders, put the tube into the
beaker of water and wait for five minutes.
4. Next, use a different syringe to add 5cm3 of a starch solution to the boiling tube.
5. Immediately mix the contents of the boiling tube and start a stop clock.
6. Use continuous sampling to record how long it takes for the amylase to break down all of the starch.To do this, use a dropping pipette to take a
fresh sample from the boiling tube every 30 seconds and put a drop into a well. When the iodine solution remains brown/orange, starch is no
longer present.
7. Repeat the whole experiment with buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken
down.
8. Remember to control any variables each time, such as concentration and volume of amylase solution, to make it a fair test.
Rate of Reaction
- Rate is a measure of how much something changes over time. For the experiment above, you can calculate the rate of reaction using the
formula, “Rate = 1000 / time”
- At pH 6, the time taken for amylase to break down all of the starch in a solution was 90 seconds.
- So the rate of reaction is “ = 11 s-1” given to 2 s.f. The units are s-1 since rate is given per unit time.
- Cells are the basic building blocks that make up all living organisms. Specialised cells carry out a particular function.
- Specialised cells are formed by a process called differentiation. This occurs during development of a multicellular organism/
- These specialised cells form tissues, which form organs, which form organ systems, which form large multicellular organisms, such as humans.
The systems inside these organisms are used for exchanging and transporting materials.
Tissues
- Tissues are a group of similar cells that group to carry out a particular function. These can include more than one type of cell. In mammals:
Organs
- An organ is a group of tissues that work together to perform a certain function.
- The stomach is made up of Muscular tissue,
Glandular tissue and Epithelial tissue.
Organ Systems
- An organ system is a group of organs working together to perform a particular
function.
- Organ systems work together to form large multicellular organisms/organisms.
Enzymes
- Living things have thousands of chemical reactions going on inside them all the time,
and these reactions need to be carefully controlled, to get the right amount of
substances.
- You can usually make a reaction happen faster by raising the temperature, but
unfortunately this makes all the reactions speed up, the useful ones and the unwanted
ones. There is also a limit to how high you can raise the temperature before cells start getting damaged.
- To solve this, living things produce enzymes, biological catalysts. Enzymes reduce the need for high temperature, and only work on their
specific reaction.
- Catalysts lower the activation energy needed to perform a chemical reaction, and this means less energy and time go into these reactions.
- Enzymes are large proteins, which are made by chains of amino acids, which are folded into unique shapes, so only work on specific reactions.
- Every enzyme has an active site with a unique shape that fits only onto the substance involved in the reaction.
- This means enzymes only work for one specific reaction.
- This is because, for the enzyme to work, the substrate has to fit into the active site. If it doesn't, the reaction won't be catalysed- “Lock and Key
model”.
, - This is simpler than how they
actually work, in reality the
active site changes shape a little
as the substrate binds to it to
get a tighter fit - the ‘induced fit’
model of enzyme action.
- Changing the temperature also changes the rate of an enzyme reaction.
- Increase in temperature results in increase in rate. If the temperature gets too high, the enzyme
could denature after some of the bonds holding the enzyme together break. With the enzyme being
denatured, the substrate for the enzyme may not fit so the reaction will not be catalysed.
- All enzymes have an optimum temperature.
- The optimum temperature for most is around the same temperature as the human body, about
37C.
- The pH also affects temperature, for the same reasons as before- it could be denatured.
- Most work at neutral pH 7, but some enzymes, such as pepsin, which breaks down proteins in the
stomach, works best at pH 2. This makes it well suited to the acidic conditions in the stomach.
Investigating the Effect of pH on Enzyme Activity
The enzyme amylase catalyses the breakdown of starch to maltose. It is easy to detect starch using
iodine solution- if starch is present, the iodine solution will change from
brown/orange to blue/black. This is how you can investigate how pH affects
amylase activity.
1. Put a drop of iodine solution into every well of a spotting tile.
2. Place a beaker of water over a Bunsen burner, on top of a tripod. Heat the
water until it is 35C, using a thermometer to measure this. Try to keep the
temperature of the water constant throughout the experiment.
3. Use a syringe to add 1cm3 of amylase solution and 1 cm3 of a buffer solution
with a pH of 5 to a boiling tube. Using test tube holders, put the tube into the
beaker of water and wait for five minutes.
4. Next, use a different syringe to add 5cm3 of a starch solution to the boiling tube.
5. Immediately mix the contents of the boiling tube and start a stop clock.
6. Use continuous sampling to record how long it takes for the amylase to break down all of the starch.To do this, use a dropping pipette to take a
fresh sample from the boiling tube every 30 seconds and put a drop into a well. When the iodine solution remains brown/orange, starch is no
longer present.
7. Repeat the whole experiment with buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken
down.
8. Remember to control any variables each time, such as concentration and volume of amylase solution, to make it a fair test.
Rate of Reaction
- Rate is a measure of how much something changes over time. For the experiment above, you can calculate the rate of reaction using the
formula, “Rate = 1000 / time”
- At pH 6, the time taken for amylase to break down all of the starch in a solution was 90 seconds.
- So the rate of reaction is “ = 11 s-1” given to 2 s.f. The units are s-1 since rate is given per unit time.
