What are cells?
Building blocks of every organism
Organisms can be…..?
Prokaryotes or Eukaryotes
I Include all animal and plant cells, have a membrane bound nucleus what cell am I ?
Describe the 5 characteristics of a eukaryotic cell
2.Has a membrane bound nucleus
4.DNA is in Multiple strands
5.Includes all multi cellular organisms-Animals and Plants.
Name the five characteristics of a prokaryotic cell
1:Has a cell wall
2.Has a cell membrane
3.Has a cytoplasm
4.Circular strand of DNA
What five characteristics do bacterial cells entail?
What is Plasmid DNA?
Small loops of extra DNA that aren’t part of the chromosome
What genes do plasmid DNA contain?
Contain genes for drug resistance
Can plasmid DNA pass between bacteria?
Yes it can
What is flagellum?
A long thin whip like structure attached to bacteria that allow them to move
What is flagellum used for?
To move the bacteria away from harmful substances (toxins), and towards nutrients and Oxygen.
Name the five components of an animal cell
What three characteristics do plant cells have that animal cells dont ?
2.Rigid cell wall
Large vacuole function
Improves cell rigidity
Maintains the internal pressure to support the cell
What is the vacuole?
Where is it found ?
The vacuole is a component of the plant cell.
It contains sell sap (a weak solution of sugar and salts)
Is found within the cytoplasm
Where photosynthesis takes place
Provides food for the plant
Contains chlorophyll (pigmentation which makes it green) which harvests the light needed for photosynthesis.
Cell wall in plants function…
Provides strength to the cell
Made from cellulose
Function of the nucleus
Contains DNA coding for a particular protein needed to build new cells
Function of the cytoplasm
Liquid substance in which chemical reactions occur
(Contains enzymes- biological catalysts- proteins that speed up the reaction)
Organelles are found it it
Cell Membrane Function…
Controls what enters and leaves the cell
Where aerobic respiration occurs- providing energy for the cell
Where are the ribosomes found ?
Found on a structure called the rough endoplasmic reticulum
What is the cell wall in bacterial cells made of ?
Where is the chromosomal circular DNA of a bacterial cell situated ?
As bacterial cells have no nucleus this floats in the cytoplasm
Name the four ways in which sperms cells are specialised to carry the males DNA to the egg cell for successful reproduction
1.Streamlined head and long tail to aid swimming
2.Many Mitochondria (where respiration happens) which supply the energy to allow the cell move.
3. The acrosome -top of the head has digestive enzymes which break down the outer layers of the membrane, of the egg cell
4. Haploid nucleus- 23 chromosomes rather than 46
Name three ways in which the egg cell is specialised to accept a single sperm cell and develop into an embryo
- Surrounded by a special cell membrane which can accept only one sperm cell (during fertilisation) and becomes impermeable following this.
2.Lots of Mitochondria to provide an energy source for the developing embryo
- Large size, and cytoplasm to allow quick repeated division as the embryo grows.
How are ciliated epithelial cells specialised to waft bacteria to the stomach ?
Long hair like process called cilia waft bacteria (trapped by sticky mucus) down to the stomach, where they are killed by stomach acid. This is one of the ways our body protects us against illness.
Enlarges extremely small structures such as the cell that can not be seen by the naked eye
Define Resolution ?
The smallest distance between two points that can still be seen as two points.
Why do electron microscopes show more detail than light microscopes ?
Electrons have a shorter wave length than visible light- they can reveal very tiny details.
They have a higher resolution.
Adding the ‘mili’ prefix to a unit divides it by….?
One metre contains …..?. (mm)
How was the nucleus discovered ?
In 1828 Robert Brown examined cells from the surface of a leaf and he noticed that each cell contained a small round blob. He called this the NUCLEUS- (meaning inner part in Latin).
One of the first people to examine cells using a microscope was?….
What did he examine and why did he call them cells ?
Robert Hooke was the first to examine cells from a microscope.
He examined bark from a cork oak tree and saw little box shapes.
He called them cells because he thought that the boxes looked like the small rooms found in monasteries at the time.
The part of the microscope where you place the slide is called…?
What part of the microscope is used to focus the image ?
The fine adjustment knob
Why is the lowest power magnification used when first examining a specimen ?
This is as the field of view will be wider increasing the number of cells you are able to see.
This is as the field of view will be wider increasing the number of cells you are able to see.
They are adapted by having membranes with many tiny folds- (microvilli). They increase the surface area of the cell - the more area for molecules to be absorbed the faster absorption happens.
How are the walls of the small intestine adapted to their function.
The walls of the small intestine have muscles to squeeze food along. The muscle cells require a lot of energy and are adapted by having many mitochondria
What are gametes ?
A gamete is a reproductive cell-egg cells and the sperm cell.
How is the embryo created ?
Two specialised cells fuse to create a cell that develops into an embryo.
Cells with two sets of chromosomes are……..?
Cells with one copy of each chromosome are………………..?
How is the ‘jelly coat’ an adaption of the egg cell.
The jelly coat protects the egg cell. It also hardens after fertilisation to ensure only one sperm cell enters the egg cell.
What nucleus does the egg cell have? and Why?
Haploid Nucleus-as they only have half the number of chromosomes.
What is the function of the cell membrane in an egg cell?
The cell membrane fuses with the sperm cell membrane. After fertilisation, the cell membrane becomes hard to stop other cells entering.
What is the role of Cytoplasm in an egg cell ?
It is packed with nutrients (to supply the fertilised egg cell with energy and raw materials) for the growth and development of the embryo.
How is the shape of a sperm cell adapted to its function ?
Streamlined shape allows rapid movement in order to reach the target egg cell.
Why do gametes need to be haploid ?
In order to maintain the number of chromosomes in the offspring.
What nucleus is present in the sperm cell ?
How is the head of the sperm cell adapted to its function ?
The tip of the head contains a small vacuole called the acrosome. It contains substances that break down substances in the egg cells jelly coat allowing the sperm cells to burrow inside.
What role does the tail have in the sperm cell ?
It waves from side to side allowing the sperm cell to swim.
What is a zygote?
A fertilised egg cell-Diploid cell. The fusion of two haploid gametes to form a zygote which is fertilisation.
Where does fertilisation occur ?
In the oviduct of the female reproductive system.
Where are egg cells transported to from the oviduct ?
Egg cells are transported towards the uterus.
Explain how cells that line the oviduct are adapted to their function of moving the egg cell ?
The oviduct cells are adapted by having hair like cilia. These are short tails that wave from side to side in order to sweep substances along.
Why are bacteria cells difficult to see with light microscopes ?
How are they made visible ?
They are difficult to see as they are very small and mostly colourless.
They are made visible to the naked eye using stains.
Your body contains more bacterial cells than human cells , True or False???
State Two sub cellular parts that bacterial cells may have but animal cells never have.
Flagella - move in a whip like motion to move the bacterium
Flexible cell wall for support- not made out of cellulose.
When you chew a piece of starchy bread for a while it starts to taste sweet. Suggest a reason for this.
This is as Saliva contains a digestive enzyme called salivary amylase. Salivary amylase converts the starch present in the food to maltose. Maltose is a sugar which is sweet in taste. So Saliva converts the starch into maltose while chewing the piece of bread.
Which monomers make up proteins ?
Which monomers make up carbohydrates ?
Monosaccharides (simple sugars) .
How do enzymes catalyse (speed up ) reactions ?
By lowering the energy of the transition state. If the activation energy is low the reaction will happen quickly, because it is easier to get over the hill.
What new theory have scientists developed to explain how enzymes and substrates fit together. What does this theory propose ?
Scientists have now come up with the induced fit model. This proposes that the active site, changes shape after the substrate has bound ensuring an even tighter fit and more precise bonding. Once the product is generated it leaves the surface of the enzyme, which turns back to its original shape.
What does the lock and key model propose ?
It shows how the enzymes active site has a very unique shape that complements the shape of a specific substrate. The active site holds the substrate tightly in order to form the product molecule.
Describe the 8 chronological steps taken in order to get a focused image of onion cells ?
- Take a thin slice of your specimen so that light can pass through.
2.Take a clean slide and use a pipette to put one drop of water in the middle- this will secure the specimen in place-Then use tweezers to place your specimen on the slide
- Add stain, if your specimen is colourless- making it easier to see
- Place a cover slip over your specimen. Press it down gently so that no air bubbles get trapped inside. Then clip the slide onto the stage.
- Select the lowest powered objective lens
- Use the coarse adjustment knob to move the stage up.
- Adjust the focus with the fine adjustment knob until you get a clear image. Position a clear ruler on the stage and measure the diameter of the area visible.
- If you need to see your specimen with greater magnification swap to see a higher powered objective lens, refocus and recalculate your field of view.
How do you draw a scientific drawing of a specimen ?
Using a sharp pencil draw outlines of the main features using clear unbroken lines. Don’t include any colouring or shading.
Make sure it’s in proportion and labelled with straight lines- that don’t cross over.
Include the scale and the magnification used.
What is a catalyst ?
A substance that increases the speed of reaction without being changed or used up in the reaction.
What is the substrate ?
The molecule changed in the reaction.
What would happen if the substrate did not fit into the active site ?
Then the reaction won’t be catalysed.
“Enzymes have special shapes so they can catalyse reactions”
Why is this called the lock and key mechanism ?
Because the substrate fits into the enzyme just like a key fits into a lock.
How do higher temperatures affect enzyme activity ?
Higher temperatures increase the rate of reaction.
What causes an enzyme to become denatured ?
If the temperature gets too hot the bonds holding the enzyme together break. This changes the shape of the enzymes active site, so the substrate won’t fit any more. The enzyme is said to be DENATURED.
How does high and low pH levels affect enzyme activity ?
Too high or too low pH interfere with the bonds holding the enzyme together. This too changes the shape of the enzyme denaturing it.
What is the optimum pH that enzymes work best at ?
Its often neutral- pH 7
Give an example that shows not all enzymes work best at the optimum pH.
Pepsin is an enzyme used to break down proteins in the stomach. It works best at pH 2- meaning it’s well suited to the acidic conditions there.
How does substrate concentration affect the rate of reaction ?
The higher the substrate the faster the reaction. This is as the likelihood that the enzyme will meet up and react with a substrate molecule increases.
How do you calculate the rate of reaction ?
E.g. At pH 6 the time taken for amylase to break down all of the starch in a solution was 50 seconds. So the rate of reaction is….1000 divided by 50 =20s[-1]
If an experiment measures how much something changes over time how is the rate of reaction calculated ?
By dividing the amount it has changed by the time taken.
How do big food molecules pass through the walls of our digestive system ?
Many molecules are too big to pass through- so digestive enzymes break them down into smaller soluble molecules allowing them to be absorbed into the bloodstream.
How do plants store energy? and How is it obtained from there ?
Plants store energy in the form of starch. When they need energy enzymes break down starch into sugars. These can then be transferred to energy and be used by the cells.
Which enzyme breaks down carbohydrates ?and what does the breakdown result into ???
Amylase (an example of Carbohydrases) breaks down starch into maltose- (simple sugars).
Which enzyme breaks down proteins ?and what does the breakdown result into ???
Proteases convert proteins into amino acids.
Which enzyme breaks down Lipids ?and what does the breakdown result into ???
Lipases breakdown lipids into glycerol and fatty acids.
Carbohydrates can be synthesised by ?
Joining together simple sugars.
What is Glycogen synthase ?
What is it used for ?
An enzyme that joins together chains of glucose molecules to make glycogen.
Glycogen is used to store energy in animals.
How are proteins made ?
By joining amino acids together.
What are Lipids made from ?
They are made from smaller units of fatty acids and glycerol.
(The gradual movement of particles from places where there are lots of them to places where there are fewer of them)
The movement of particles from an area of higher concentration to an area of lower concentration.
In what state of matter does diffusion take place ? And why ?
In both liquids and gases.
This is because the particles in these substances are free to move about.
If something moves from an area of higher concentration to an area of lower concentration it is said to have moved down a ???
Why is osmosis a special case of diffusion??
It only involves water 💦 molecules
Define osmosis ???
The movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration.
What is meant by partially permeable membrane ??
A membrane through which only tiny molecules can pass through and bigger molecules such as sucrose can’t.
Explain the net movement of water in osmosis ??
As there are more water molecules on one side than the other, there’s a steady net flow of water into the region with fewer water molecules - (into the more concentrated solute solution).
This means the solute solution gets more dilute- the water acts like it’s trying to even up the concentration either side of the membrane.
How is active transport different from diffusion ?
As particles in active transport are moved up a concentration rather than down.
And the process requires energy unlike diffusion which is a passive process.
State an example of active transport in the digestive system.
Glucose is moved from a low concentration in the small intestine to a higher concentration in the blood.
What experiment can be done to investigate osmosis ???
Putting potato cylinders into different concentrations of sucrose solution to see what effect different water concentrations have on them.
The higher the concentration of the sucrose solution, the lower the water concentration. True or False ??
Describe the step by step procedure of the osmosis In potato slices practical.
1.Prepare sucrose solutions of different concentrations ranging from pure water to a very concentrated sucrose solution.
2. Use a cork borer to cut a potato in the same sized pieces (the pieces need to be about 1cm in diameter and preferably from the same potato)
3. Use a mass balance to measure the mass of each potato cylinder
4. Place one potato cylinder in each solution
5. Leave the potato cylinders in the solution for atleast 40 mins - (making sure they all get the same amount of time).
6. Remove the cylinders and pat dry gently with a paper towel to remove excess water so a more accurate measurement is gained.
7. Weigh each potato cylinder again and record your results
8. Everything in this experiment should be kept the same apart from the sucrose solution concentration or the results won’t be valid.
How do you calculate the percentage change in mass ?
Final mass- initial mass ÷initial mass ×100
E.g. a group of cylinders weighed 13.2g at the start of the experiment. At the end they weighed 15.1g. calculate the percentage change in mass.
15.1- 13.2 ÷ 13.2× 100= 14.4%
What do the positive and negative of percentage change in mass tell you ?
The positive result tells you the potato cylinders gained mass. If the answer was negative than the potato cylinders lost mass.
Give two examples of processes that are controlled by enzymes in the human body.
- Breaking down food particles during digestion
- Destroying toxins
What happens to someone who does not make phenylalanine hydroxylase ?
Phenylalanine is found in foods that contain proteins. Absence of phenylalanine hydroxylase results in intolerance to the dietary intake of the essential amino acid. This causes the build up of phenylalanine levels in the body. This build up can harm the central nervous system and cause brain damage.
What is the heel prick test ?
The heel prick test takes a small amount of blood to test for several factors including the enzyme phenylalanine hydroxylase. This enzyme breaks down an amino acid called phenylalanine. Babies are given the heel prick test before they are a week old. A few babies are born without the ability to make the enzyme. 🥺😨
What are enzymes and what are they made of ?
Enzymes are proteins comprised of amino acids linked together In one or more polypeptide chains.
What does a blue black solution indicate when iodine solution is added to a food ?
It indicates the presence of starch
What would happen if you dropped iodine solution onto the soft part of a ripe banana ?
There would be no reaction. This is as the amount of starch is reduced and amyloplasts (what stores starch) are no longer present.
Why do bananas taste sweeter as they ripen ?
As bananas ripen, enzymes break down starch into smaller carbohydrates, including sugars such as sucrose and glucose.
What test is done to check whether reducing sugars- (smallest sugars, including glucose and fructose) are present in the food or not?
Benedict’s solution is added into a sample solution in the test tube and heated in a water bath for 5 minutes. The test tube is then taken out of the water bath and the colour is observed. A positive test will chow a colour change from blue to orange or brick red.
We can use iodine to test for the presence or absence of…..?
and how is this experiment carried out ?
To test for the presence or absence of starch in a food sample.
Add drops of iodine solution to the food sample. A positive test will show a colour change from orange- brown to blue-black.
What test is done to indicate the presence of protein in food ?
Drops of biuret solution are added to the food sample. A positive test will show a colour change from blue to purple.
The ethanol emulsion test is used to test ……?
and how is this test carried out?
It used to test for fats and oils (lipids).
The food sample is mixed with ethanol and shaken. It is then added to an equal volume of cold water. A positive test will show a cloudy emulsion forming.
How can the amounts of energy in food be measured ?
It can be measured by burning it in a calorimeter.
Explain how the calorimeter is used to measure the amount of energy in a piece of food.
A piece of food is burned and the released energy is used to heat a known quantity of water. The temperature change of the water is then used to determine the amount of energy in the food.
What happens when iodine is added to cooked rice ?
Rice is rich in starch when drops of iodine are added to it the rice turns-blue-black.
What is the active site ?
Where the substrate of the enzyme fits at the start of a reaction.
Why does amylase not break down proteins ?
Salivary amylase does not break down proteins because it does not have the required 3D shape to catalyse the breakdown of proteins. Every enzyme has a pretty specific substrate, and the substrate physically interacts with the enzyme during catalysis.
Why do enzymes work slowly when the temperature is below the optimum ?
At low temperatures enzyme activity is low because the enzyme and substrate molecules have less kinetic energy so there are fewer collisions between them.
Why do enzymes work slowly when the temperature is above the optimum ?
This is because the enzyme starts to lose its shape which leads to the active site no longer fitting with the substrate.
Many human enzymes have a optimum temperature of around ….?
Why do red blood cells burst when put in pure water ?
Distilled water is a hypotonic solution, meaning it has less solute in it than a red blood cell. In a hypotonic environment water rushes into the red blood cell in an attempt to reach equilibrium causing the cells to expand and burst.
How are cells that carry out active transport adapted to their function ?
They usually have more mitochondria and Proteins embedded in the cell membrane help move substances across the membrane.
Why does sorbitol cause diarrhoea ?
This is as it is poorly absorbed by the small intestine and may produce an osmotic diarrhoea if ingested in large amounts.
Plants in salty soil would have problems absorbing water through their roots. Explain why ?
Why do muscle cells contain many Mitochondria ?
Muscle cells require large amounts of energy for contraction. This energy is supplied by respiration in mitochondria.
Why do all plant cells contain mitochondria but only some contain chloroplasts ??
Mitochondria release energy and all cells need energy but only leaf and stem cells are exposed to light and so have chloroplast for photosynthesis.
What is the difference between a cell membrane and a cell wall?
What is the difference between a cell membrane and a cell wall?
The egg cell is much larger than the sperm cell. Give a reason to explain why ?
The egg cell contains nutrients in the cytoplasm to supply the growing embryo.