Revision 1 Flashcards
Eukaryotic Cells
1 mark
Complex Cells
Examples of a Eukaryotic Cell
2 marks
- Animal
2. Plant
Prokaryotic Cells
1 mark
(Small) Simple Cells
Example of a Prokaryotic Cell
1 mark
- Bacterium
Mitochondria
1 mark
Subcellular structure where most of the reactions for cellular respiration take place
- Powerhouse of the cell; provides energy.
Vacuole
1 mark
Subcellular structure that maintains the internal pressure in a plant cell.
Similarities between a Bacterial Cell and a Plant Cell
4 marks
Both have;
- a Cell Membrane
- a Cell Wall
- Cytoplasm
- Ribosomes
Differences between a Bacterial Cell and a Plant Cell
5 marks
Plant Cells have Chloroplasts + Mitochondria, Bacteria don’t.
Chromosomes of Plant Cells are contained within a Nucleus - Bacteria have a Chromosomal DNA that floats freely in Cytoplasm.
Bacterial Cells may contain small loops of extra DNA called plasmids.
Cell Membrane
2 marks
- Holds cell together
- Controls what enters + leaves.
Nucleus
2 marks
Contains genetic material that controls Cell activities.
Ribosomes
2 marks
Involved in translation of genetic material in the synthesis of proteins.
Structural differences between a Plant Cell and an Animal Cell
(3 marks)
Plant cell has;
- a Cell Wall
- Large Vacuole
- Chloroplasts
Where are ciliates epithelial cells found?
2 marks
On the surface of organs.
2 functions of an egg cell
4 marks
- Carry the female DNA
- Provide nutrients to the embryo in the early stages.
Why do Sperm Cells contain a large number of Mitochondria?
3 marks
To provide the energy (from respiration) needed to swim to the egg.
Why is it important that the Egg + Sperm Cells are Haploid?
4 marks
So when an Egg Cell + a Sperm Cell nucleus combine (at Fertilisation) the resulting Cell will have the right number of Chromosomes.
Cells with only half the number of Chromosomes of a normal body Cell
(1 mark)
Haploid Cells
Cells with the full number of Chromosomes of a normal body Cell
(1 mark)
Diploid Cells
Describe how ciliated Epithelial Cells are adapted for moving substances.
(3 marks)
They have Cilia, which beat to move substances in one direction along the surface.
Why does the structure of an Egg’s Cell Membrane change after Fertilisation?
(2 marks)
To stop more Sperm entering - making sure that the offspring end up with the right amount of DNA.
Parts of the Sperm Cell - Explained
6 marks
Tail - allows the Sperm to swim towards an Egg Cell.
Acromosome - stores the Enzymes the Sperm needs to digest it’s way through the membrane of an Egg Cell.
What is the purpose of the fine adjustment knob on a light microscope?
(2 marks)
To focus the lens until a clear image of what’s on the slide appears.
True or false? Electron microscopes have a smaller magnification, but a higher resolution than light microscopes.
(3 marks)
False. Electron microscopes have both a higher resolution + a higher magnification than light microscopes.
What is resolution?
1 mark
The ability to distinguish between 2 points.
What is magnification?
1 mark
Process of making something look larger.
Describe how you would put a cover slip onto a specimen on a slide so that it’s ready to be viewed under a light microscope.
(6 marks)
The cover slip should be placed at one end of the specimen + held at an angle with a mounted needle.
It should then be carefully lowered onto the slide + pressed down gently so that no air bubbles are trapped under it.
How has Electron Microscopes increased our understanding of Cells?
(7 marks)
Their high magnification + high resolution has allowed biologists to see very small structures in detail, like the internal structure of mitochondria + chloroplasts.
This has allowed biologists to better understand how cells work + has given us a greater understanding of the role of subcellular structures.
What to remember when drawing a scientific drawing of a Cell?
(7 marks)
- Labels of important features
- A scale
- Magnification used
- Make sure lines do not cross over
- Do not shade
- Make lines clear; using a sharp pencil
Is a picometer smaller or larger than a nanometer?
5 marks
Smaller -
a picometer is 10 ^-12m (Small -12)
a nanometer is 10^-9m (Small -9)
Idina knows the eyepiece lens + objective lens magnification of her microscope.
What formula should she use to calculate the microscopes total magnification?
(3 marks)
Total magnification = eyepiece lens magnification x objective lens magnification.
A specimen is 100 μm wide. Calculate the width of the image of the specimen under a magnification of x 200. Give your answer in mm.
Use the equation:
magnification = image size/real size
(10 marks)
Image size = magnification x real size
= 200 x 100 μm = 20 000 μm
To convert micrometers (μm) to millimetres (mm) divide by 1000
= 20 000 μm/1000 = 20mm
Ans: 20mm
How can you Convert Micrometers (μm) to Millimeters (mm)?
3 marks
Divide by 1,000
or x 10^-3.
How can you Convert Millimeters (mm) to Micrometers (μm)?
3 marks
Multiply by 1,000
or x 10^3.
A student uses a calculator to calculate the real size of a protists that has an image size of 214 μm under a microscope with x18 magnification.
Estimate the real size of the protist without a calculator.
(8 marks)
First round the Numbers to one significant figure.
Image size = 200 μm
Magnification = x 20
Real size = 200 / 20 = 10 μm
Ans: 10 μm
Why might the student want to estimate the size of the protist as well as calculate it with a calculator?
(1 mark)
To check the answer they got with the calculator is sensible.
How can you convert Picometers (pm) to Micrometers (μm)?
2 marks
Divide by 100,000,0
or x 10^-6.
How can you convert Micrometers (μm) to Picometers (pm)?
3 marks
Multiply by 100,000,0
or x 10^6.
How can you convert Nanometers (nm) to Millimeters (mm)
3 marks
Multiply by 100, 000,0
or x 10^6.
How can you convert Millimeters (mm) to Nanometers (nm)?
3 marks
Divide by 100, 000,0
or x 10^-6.
How can you convert Millimetres (mm) to Picometers (pm)?
3 marks
Divide by 100,000,000,0
or x 10^-9.
How can you convert Picometers (pm) to Millimetres (mm)?
3 marks
Divide by 100,000,000,0
or x 10^-9.
How can you convert Nanometers (nm) to Picometers (pm)?
3 marks
Divide by 1,000.
or 10^-3.
How can you convert Picometers (pm) to Nanometers (nm)?
3 marks
Multiply by 1,000.
or 10^3.
Standard forms for converting units into Metres (m)
12 marks
Milli (mm)- x 10^-3
Micro (μm)- x 10^-6
Nano (nm)- x 10^-9
Pico (pm)- x 10^-12
How can you convert Micrometers (μm) to Nanometers (nm)?
3 marks
Multiply by 1,000
or x 10^3.
How can you convert Nanometers (nm) to Micrometers (μm)?
2 marks
Divide by 1,000
or x 10^-3.
How do Enzymes affect the rate of a reaction?
2 marks
Enzymes increase the rate of a reaction (they act as Biological catalysts).
What is an active site of an enzyme?
3 marks
The part of the enzyme which joins on to its substrate to catalyse the reaction.
True or false? Enzymes have a high specificity for their substrate.
(2 marks)
True. Enzymes usually only work with one substrate.
A graph shows the effect of substrate concentration on the rate of an enzyme-catalysed reaction.
Why does a further increase in substrate concentration have no effect on the rate of reaction after its peak?
(4 marks)
After it’s peak there are so many substrate molecules that all the active sites of the enzymes are full - adding more substrate makes no difference to the rate of the reaction.
Apart from substrate concentration, give 2 variables that affect the rate of an enzyme-catalysed reaction.
(3 marks)
Temperature + pH
all enzymes have an optimum temp and pH that they work best at
Describe what happens to an enzyme when it is denatured.
4 marks
Some of the bonds holding the enzyme together break + the shape of its active site changes - substrate then won’t fit so the enzyme can’t catalyse reactions any more.
True or false?
pH is the dependent variable in an experiment investigating how pH Affects enzyme activity.
(5 marks)
False.
pH is the independent variable - the variable that you change in order to see what effect it has on another variable. The dependent variable (the variable you measure when you change the independent variable) is enzyme activity.
In an experiment investigating how pH Affects amylase activity, what would you use to test for the presence of starch?
(1 mark)
Iodine Solution
A student is investigating the effect of pH on the rate of amylase activity.
Suggest how the student could control the temperature of the amylase + starch solution during the experiment.
(5 marks)
The student could put a test tube containing the solution in a beaker of Water over a Bunsen burner + use a thermometer to help keep the water at a constant temperature.
Alternatively, the student could use an electric water bath.
The student uses continuous sampling to record how long it takes for the amylase to break down all of the starch.
What is continuous sampling?
(4 marks)
Continuous sampling - when lots of samples are taken at regular intervals over a particular time period.
A scientist carried out an enzyme-controlled reaction. After 100 seconds, 45 cm^3 of the product had been produced.
Calculate the rate of reaction in cm^3/s.
Use the equation:
Rate of reaction = amount of product formed / time
Rate of reaction = amount of product formed / (divided by) time
= 45 / 100
= 0.45cm^3/s
What happens if the temperature is too hot while investigating the effect of pH on enzyme activity?
(2 marks)
The Enzyme will denature
Which type of molecule are proteins broken down into?
1 mark
Proteins are broken down into Amino acids.
What type of Enzyme breaks down Proteins?
1 mark
Proteases
Rice contains a lot of the carbohydrate starch.
Name the type of Enzyme that will break down starch during digestion.
(1 mark)
The starch will be broken down by carbohydrases.
How are carbohydrates synthesised?
3 marks
Simple sugars are joined together to form carbohydrates in a Process catalysed by enzymes.
Why is it important that organisms are able to break down big molecules into smaller molecules?
(7 marks)
E.g. Big molecules are unable to pass through the walls of the digestive system + can’t be absorbed into the bloodstream.
Smaller molecules can pass through + be absorbed, which means they can then pass into cells + be used for growth and other life processes.
Lipase is any enzyme that catalyses the hydrolysis of fats (lipids) breaking it down into fatty acids + ________.
(1 mark)
Glycerol
Lipids are made up of
3 marks
2 fatty acids + Glycerol
Perform essential roles in digestion, transport + processing of dietary lipids (e.g. triglycerides, fats, oils) in most, if not all, living organisms.
(1 mark)
Lipase
Lipids are
2 marks
Fats + oils.
Carbohydrase enzymes break down starch into?
1 mark
Sugars
True or false?
Oxygen entering the Blood from the lungs is an example of Osmosis.
(3 marks)
False.
This happens by diffusion. Osmosis involves the movement of water.
What type of membrane is needed for osmosis to happen?
3 marks
A partially permeable one (it has small holes in it, so only tiny molecules can pass through).
When plants lose water, they start to wilt.
Explain why most plants will wilt if the soil they are growing in is flooded with salty sea water?
(6 marks)
The sea water has a high concentration of salt, so water concentration in the soil will be lower than in the plant.
This means water would move by osmosis from Plant to the soil (from a higher concentration to a lower concentration), causing the plant to lose water + wilt.
Oxygen diffuses from the blood stream into muscles. During exercise, O2 is used up in the muscles faster than when a person is at rest.
Suggest how the rate of O2 diffusion might differ when a person is running vs when they are sitting.
(5 marks)
The diffusion rate will be greater when a person is running vs when they are sitting.
- This is because there will be a lower concentration of O2 in the muscles (as it is used up quicker) meaning there will be a greater concentration gradient + so a faster rate of diffusion.
How does substances travelling (across a cell membrane) via Active Transport move?
(5 marks)
Against the concentration gradient to an area of higher concentration from an area of lower concentration - cellular energy (usually ATP) + carrier proteins are required.
Features of Diffusion
4 marks
Movement of a substance(s) down the concentration gradient from an area of high to an area of low concentration.
Osmosis Features
4 marks
Movement of a water molecules against the concentration gradient from an area of low to an area of high concentration.
Features of Passive Transport
6 marks
Movement of substances down the concentration gradient from an area of high to an area of low concentration - does not require the input of energy.
- Takes place when molecules diffuse across the cell membrane by travelling through specific transport proteins
3 Common types of Passive Transport
3 marks
Simple diffusion, osmosis + facilitated diffusion.
Simple Diffusion vs Facilitated Diffusion
6 marks
Simple Diffusion - movement of molecules through a cell membrane without using the channels formed by integral membrane protein.
Facilitated Diffusion - movement of molecules through those channels.
Protein Channels
8 marks
Special arrangement of amino acids (proteins) which embeds in the cell membrane, providing a hydrophilic passageway for water + small, polar ions - and help them move along.
Transport proteins
3 marks
Size + shape which excludes all but the most specific molecules.
Active transport requires assistance from carrier proteins, which do what?
(2 marks)
Change conformation when ATP hydrolysis occurs.
ATP Hydrolysis
8 marks
When an appreciable amount of energy (found in ATP) is released when a high-energy phosphoanhydride bond is broken in a catabolic hydrolysis (water-mediated breakdown) reaction.
Example of ATP Hydrolysis
3 marks
Found in the muscles, by producing work in the form of mechanical energy.
What does ATP stand for
2 marks
Adenosine Triphosphate
What are examples of carrier proteins within our Cells?
2 marks
Sodium potassium pump + glucose transporters
What is ATP?
3 marks
Small, relatively simple molecule - the main energy currency of cells.
What is the energy released by hydrolysis (breakdown) of ATP is used to do?
(2 marks)
Power many energy-requiring cellular reactions.
Structurally, ATP is what?
2 marks
An RNA nucleotide that bears a chain of three phosphates.
Carrier Proteins
10 marks
Allow chemicals (or Ions/Molecules) to cross the membrane against a concentration gradient or when the phospholipid bilayer of the membrane is impermeable to a chemical.
These proteins are specific to what they allow to cross the membrane depending on the size + shape of the Molecules
ADP stands for
2 marks
Adenosine Diphosphate
Facilitated Diffusion
7 marks
Passive movement of molecules, down the concentration gradient across the cell membrane via the aid of a membrane protein.
- They usually move from an area of high concentration to an area of low concentration but can move freely in and out of a Cell Membrane
Facilitated Transport + Energy
8 marks
Being passive, facilitated transport does not directly require chemical energy from ATP hydrolysis in the transport step itself;
rather, molecules + ions move down their concentration gradient reflecting its diffusive nature.
Active Transport + Carrier Proteins
4 marks
The carrier proteins used in Active Transport are different than the ones seen in facilitated diffusion, as they need ATP in order to change conformation.
Channel proteins are not used in Active Transport because
2 marks
Substances can only move through them along the concentration gradient.
How does water concentration change as solute concentration increases?
(4 marks)
The water concentration of a solution decreases as the solute increases.
How would the mass of a potato cylinder change if you put it in a solution that has the same water concentration as the fluid inside the potato?
(2 marks)
There would be no change in the mass of the potato cylinder.
Yashvi has 2 potato cylinders. The fluid inside the Potato Cells has a concentration of 0.3 mol/dm^3. She weighs the 2 cylinders + places one into a beaker of pure water + the other into a beaker of 1.0 mol/dm^3 Glucose Solution. After 24 hours, she removes the cylinders, dries them, + measures their final mass.
Explain how the mass of each potato cylinder will have changed after 24 hours.
(10 marks)
The mass of the cylinder in pure water will have increased because the water will have moved by Osmosis from an area of higher (pure water) to an area of lower water concentration (the potato). The mass of the cylinder in the Glucose will have decreased, as water will have moved by Osmosis from an area of higher (the potato) to an area of lower water concentration (Glucose solution)
The potato cylinders weren’t dried properly during this experiment, so the excess water added to the mass of the potato.
How could Yashvi reduce the effect of errors like this?
(3 marks)
Repeating the experiment + calculating a mean percentage change in mass.
The mass of a group of potato cylinders has increased from 12g to 15g.
Calculate the percentage change in mass.
(15 marks)
Percentage change in mass =
final mass - initial mass
—————————— x 100
Initial mass
= 15 - 12
_________ x 100 = 0.25 x 100 = 25%
12
When calculating the percentage change in mass of Plant tissue - an increase in mass will give you
(2 marks)
A Positive percentage change.
When calculating the percentage change in mass of Plant tissue - a decrease in mass will give you
(2 marks)
A Negative percentage change.
Calculating a change in mass - percentage
7 marks
Final mass - initial mass
Divide by initial mass
Multiply by 100
Calculating the mean/average
3 marks
Add all numbers
Divide by how many numbers there are.
Calculating the median
4 marks
Line up numbers in numerical order
Find middle number - this is the median.
Calculating the median with 2 ‘middle Numbers’
6 marks
Line up numbers in numerical order
Find middle numbers - add them
Divide your answer by 2.
Calculating the Mode of Numbers
2 marks
The mode is the most common number found in a list.
Calculating the Range
7 marks
Find the largest + the smallest value of a group of numbers.
Subtract the smallest from the largest - the result is the Range.
What is Mitosis? What is it used for?
8 marks
Mitosis is the stage of the Cell Cycle when the Cell divides. Organisms use mitosis to grow or replace Cells that have been damaged.
Some organisms use mitosis to reproduce (asexual reproduction).
Name the 4 stages of the Cell Cycle that are part of Mitosis.
(4 marks)
Prophase, Metaphase, Anaphase + Telophase.
What happens during Cytokinesis?
4 marks
The Cytoplasm + Cell Membrane divide to form 2 separate Cells.
Describe the processes that led to the Prophase stage of the Cell Cycle.
(9 marks)
The Cell grew + increased the amount of subcellular structures (e.g mitochondria + ribosomes).
It then duplicated it’s DNA. The DNA formed X-shaped chromosomes. Each arm of a chromosome (chromatid) is an exact duplicate of the other.
How will the DNA of the cells forming in Telophase compare to the DNA in the original Cell from which they were formed?
(2 marks)
The DNA in the Cells will be identical to the DNA in the original Cell.
A normal human body contains 23 pairs of chromosomes.
How many chromosomes would be in each new Human Cell formed by mitosis?
(4 marks)
Each Cell will have 46 chromosomes (23 pairs).
What happens following the stage in Anaphase where chromosomes are pulled apart and moved to opposite ends of the Cell?
(3 marks)
2 nuclei form (during Telophase)
Cytoplasm, Organelles + Cell Membrane divide, forming 2 new Cells during what phase of Mitosis?
(1 mark)
Cytokinesis
The Process of Interphase
6 marks
Cell performs its normal functions, + grows in size. Organelles are replicated.
Cell synthesis takes place - the cell pauses its normal functioning. Resources dedicated to replicating the DNA.
Name the 2 methods that plants use to grow.
2 marks
Cell division + Cell elongation.
What does it mean if a baby measures at the 50th percentile for weight?
(6 marks)
It means the baby is of average weight for it’s age - roughly 50% of babies it’s age are heavier and 50% of babies it’s age are lighter.
Why is Cell differentiation important?
6 marks
Cell differentiation allows Cells to become specialised for a specific job
Having specialised Cells allows Multicellular organisms to work more efficiently.
How does the ability to differentiate differ between Plant Cells + Animal Cells?
(5 marks)
The ability to differentiate is lost at an early stage in most Animal Cells (after they become specialised), but lots of Plant Cells don’t ever lose this ability.
What are growth charts used for?
3 marks
They are used to assess a child’s growth over time, so any problems can be highlighted.
Describe how Cancer can develop from changes in a Cell.
8 marks
If there is a change in 1 of the genes that controls Cell Division, the Cell may start dividing uncontrollably.
This can result in a mass of abnormal cells called a Tumour. If a Tumour invades + destroys surrounding tissue it is called Cancer
Tumour
2 marks
A mass of abnormal cells.
What is an embryonic stem cell?
4 marks
An undifferentiated cell found in early human embryos which has the potential to divide + produce any kind of cell.
Where can Stem Cells be found in an adult human? What do they do?
(4 marks)
E.g. Bone Marrow.
They are used to replace damaged cells, such as blood or skin cells.
What type of plant tissue contains Stem Cells?
2 marks
Meristem tissue (this is where growth occurs).
Describe 2 potential risks of using Stem Cells in Medicine.
7 marks
E.g. if donor Stem Cells are contaminated with a virus, the virus could be passed in to the recipient. If the cells divide too quickly inside the patient, a Tumour May develop. If the transplanted Cells aren’t grown using the patients own stem cells, their body might reject them.
Describe 1 example of how adult stem cells can be used to cure a disease.
(5 marks)
E.g. Sickle Cell Anaemia can sometimes be cured with a Bone Marrow transplant. The Bone Marrow contains adult Stem Cells which produce new healthy Blood Cells.
Heart attacks are caused by the blockage of Coronary Arteries that carry Oxygen to the heart. This can result in damage or death of Heart muscle.
Suggest how embryonic Stem Cells could potentially be used to treat a patient after a Heart Attack.
(7 marks)
Embryonic Stem Cells could be made to develop into Heart Muscle Cells. These could repair the damaged tissue or replace the damaged cells after a Heart Attack.
What are the benefits of using Stem Cells in Medicine?
11 marks
Treating leukaemia - chemotherapy + radiotherapy destroy WBC’s in the patient’s body, stopping their bone marrow producing new blood cells.
A bone marrow transplant containing stem cells from a matching donor allows healthy blood cells to be made in the patient.
What are the risks associated with the use of Stem Cells in Medicine?
(10 marks)
Risk of infection from the environment (and the donor) as chemotherapy + radiotherapy leave the patient with no immune system.
Stem cells may divide in an uncontrolled manner leading to the formation of tumours/the development of unwanted cell types.
Transfer of viruses or diseases from other animals.
True or false? Muscles and Glands are examples of Receptors.
2 marks
False. They are effectors.
In humans, what does the Central Nervous System (CNS) consist of?
(2 marks)
The Brain and Spinal Cord.
Which type of Neurone carries impulses from the CNS to Effectors?
(1 mark)
Motor Neurone
What is the benefit of an Axon having a Myelin Sheath?
4 marks
A Myelin Sheath acts as an electrical insulator, which speeds up the movement of electrical impulses along the Axon.
What is a Myelin Sheath?
8 marks
An insulating layer (Sheath), made up of protein and fatty substances, that forms around nerves, including those in the brain + spinal cord
- which allows electrical impulses to transmit quickly and efficiently along the nerve cells.
Describe the difference in function between Dendrons and Axons.
(5 marks)
Dendrons carry nerve impulses towards the Cell body. Axons carry nerve impulses away from the Cell body.
Compare the difference in structure of a sensory and a motor neurone.
(9 marks)
Sensory Neurones have 1 long Dendron + 1 short Axon.
Motor Neurones have many short Dendrites + 1 long Axon.
Describe the structure and function of a Relay Neurone.
9 marks
A Relay Neurone has many short Dendrites that carry nerve impulses from Sensory Neurones to the Cell body.
It has an Axon that carries nerve impulses from the Cell body to Motor Neurones.
How many Communication systems does the human body have?
4 marks
2 communication systems - that allow us to respond to any changes in our environment.
What is the job of the nervous system?
3 marks
Uses nerve impulses (electrical impulses) to react quickly to a stimulus.
What is the the job of the Hormonal System?
3 marks
Uses hormones to react slowly to a stimulus.
What is the speed of the Nervous System?
1 mark
Fast
What is the speed of the Hormonal System?
1 mark
Slow
What is the Nature of the Response of the Nervous System?
1 mark
Electrical impulses
What is the Nature of the Response of the Hormonal System?
3 marks
Hormones/Chemicals that travel in Blood.
What is the job of the CNS?
4 marks
Controls and coordinates responses between Receptors and Effectors.
What are Dendrites?
6 marks
Projections of a neuron (nerve cell) that receive signals (information) from other neurons, through electrochemical signals.
What is the transfer of information from one neuron to another (in Dendrites) achieved through?
(3 marks)
Electrochemical signals - Made up of Chemical signals and electric impulses.
What are Electrochemical signals?
5 marks
Made up of Chemical signals and electric impulses - they transfer information from Neurone to Neurone where it is received in the Dendrites.
What are Stimuli?
3 marks
Stimuli are changes in our environment that we respond to and are detected by receptors.
What are Receptors and what do they do?
11 marks
Proteins or glycoprotein that bind signaling molecules known as first messengers, or ligands.
They can initiate a signaling surge, or chemical response, that induces cell growth, division, and death or opens membrane channels
What are receptors?
3 marks
Proteins or glycoprotein that bind signaling molecules (ligands).
What is the job of Receptors?
8 marks
Bind ligands, initiate a signaling cascade, or chemical response - that induces cell growth, division and death or opens membrane channels.
What are Ligands?
6 marks
Something that binds with a biological molecule to form a complex and produce some effect.
In neuroscience, ligand frequently refers to substances that bind to receptors.
Different receptors are sensitive to, what?
3 marks
Different stimuli (e.g. receptors in the eye are sensitive to light).
What is the job of the Nerve cell/Neurone?
5 marks
Carries information in the form of nerve impulses from the receptor to the coordinator (an effector).
What is The Coordinator and what does it do?
3 marks
Brain or Spinal Cord – determines whether or not to respond to the stimulus.
What is an Effector?
3 marks
Muscle or Gland that can bring about a response.
Parts of the Nervous System;
In order
(11 marks)
Stimulus Receptors (e.g sense organs) Sensory Neurones Coordinator (e.g CNS) - Relay Neurones Motor Neurones Effectors (e.g muscle glands) Response
Where are Relay Neurones found?
4 marks
CNS (Brain + spinal cord) and Visual System.
How do Relay Neurones interact with the
CNS and Visual System they are found in?
(7 marks)
- Receive signals from a Neurone
- Pass it on to an interneuron within the systems
- Resulting in - signal being passed to a motor neurone
- Thus driving the reaction to the stimulus (the effectors react)
How can the Relay Neurones be differentiated from other Neurones?
(3 marks)
By observing their short Dendrites and either long or short Axons.
What are Sensory Neurons and what do they do?
5 marks
Nerve Cells within the nervous system responsible for converting external stimuli from the organism’s environment into internal electrical impulses.
Example of the work of Sensory Neurones
3 marks
Some sensory neurons respond to tactile stimuli and can activate motor neurons in order to achieve muscle contraction.
What are Motor Neurones and what do they do?
10 marks
MN’s of the spinal cord are part of the (CNS) and connect to muscles, glands and organs.
They transmit impulses from the spinal cord to skeletal and smooth muscles and so directly control all of our muscle movements.
What is an Interneuron?
4 marks
a neuron which transmits impulses between other neurons, especially as part of a reflex arc.
Explain the Nervous System
22 marks
The Receptors bind ligands, initiate a signaling cascade, or chemical response to the SN’s.
Which converts external stimuli from the organism’s environment into internal electrical impulses. RN’s found in the CNS receives signals from a Neurone - Passes it on to an interneuron within the systems.
Resulting in a signal being passed to a MN. Which transmits impulses from the spinal cord to skeletal + smooth muscles, controlling all of our muscle movements. The effectors then respond to the Receptors.
What part of the eye is sensitive to light?
1 mark
Receptors
What are eyes?
3 marks
Specialised sense organs containing receptors sensitive to light.
Where is a focused image produced in the eye, under different light conditions?
(1 mark)
Retina
Conjunctiva
4 marks
Thin, transparent protective outer covering that prevents entry of microorganisms.
What is the Cornea and what does it do?
4 marks
Transparent part at front of eye that allows light to enter. It also causes slight bending/refraction of light.
Pupil
2 marks
Space in the iris that allows light into the eye.
Iris
2 marks
Controls how much light enters the eye by changing its diameter.
Lens
3 marks
Bends/refracts light towards the retina.
Aqueous humour
3 marks
Fluid in front of the lens that helps maintain the shape of the eye and lens.
Vitreous humour
4 marks
Fluid behind the lens that helps maintain the shape of the eye and lens. It also keeps the retina against the wall of the eye.
Retina
2 marks
Contains light sensitive receptor cells.
Optic nerve
3 marks
Contains neurones that carry information from the eye to the brain
What takes place as light passes through the cornea?
3 marks
Refraction takes place - more refraction occurs when the light passes through the lens.
What can be done in order to focus light on the retina?
2 marks
Thickness of the lens can be adjusted.
What happens to the lens when looking at a distant object?
4 marks
Lens is thin as little adjustment is needed to focus light onto the retina.
What happens to the lens when focusing on nearby objects?
4 marks
Lens is thick to provide additional refraction to focus light on the retina.
What is the Ciliary muscle?
2 marks
A circular ring of muscle, surrounds the lens.
What attaches the Lens to the Ciliary muscle?
1 mark
Suspensory Ligaments
What happens to the Eye when focusing on a distant object?
4 marks
Muscle relaxes and it’s diameter becomes wider - as the suspensory ligaments tighten, pulling the Lens thinner.
What happens to the Eye when focusing on a nearby object?
5 marks
Muscle contracts, diameter becomes smaller; the Suspensory Ligaments slacken causing the Lens to go back to its normal thicker shape.
What can happen when too little/too much light enters the eye?
(4 marks)
Can damage the light sensitive receptor cells in the retina.
What happens to the eye pupil in dim light?
2 marks
Pupil becomes larger to allow as much light as possible to enter.
What happens to the eye pupil in bright light?
2 marks
Pupil becomes smaller to restrict the amount of light entering.
What connects the Receptors & Effectors to the CNS?
1 mark
Neurones
What is the Function of Neurones?
2 marks
Transmit electrical impulses across the NS quickly.
How are Neurones adapted to transmit impulses across the NS?
6 marks
Contains a Cell body, Axon, Myelin Sheath, Branched ends of Axon + smaller branches coming from the Cell body.
How is the Neurones Cell body adapted to transmit electrical impulses?
(2 marks)
Contains cytoplasm and nucleus.
What is the (Neurones) Axon and how is it adapted to transmit electrical impulses?
(4 marks)
Long extension of the cytoplasm (can be up to 1m).
Means nerve impulses can be transmitted to the extremities by 1 cell.
What is the (Neurones) Myelin Sheath and how is it adapted to transmit electrical impulses?
(4 marks)
Myelin sheath is a fatty layer that surrounds the axon.
Acts as an insulator and speeds up nerve impulses.
How are the (Neurones) Branched ends of Axon and the smaller branches coming from the Cell body - adapted to transmit electrical impulses?
(4 marks)
Allow the neurone to make connections with many other neurones.
What is a Synapse?
2 marks
A synapse is the connection between 2 Neurones.
How are nerve signals transferred across a synapse?
5 marks
Neurotransmitters (Chemicals) diffuse across the Synapse and set off a new electrical impulse in the next Neurone.
Reflexes do not involve conscious parts of the brain. Why is this advantageous?
(3 marks)
It reduces the chance of an injury, as it means that reflexes can be rapid and automatic.
A fly flies towards Vlad and he blinks automatically.
What is the stimulus for this reflex?
(1 mark)
The fly
A gardener is pulling up weeds when she gets stung by a nettle. A reflex action causes her to immediately move her hand away from the nettle.
What is the effector in this reflex action?
(2 marks)
The muscles in her hand.
Describe the pathway taken by the body’s automatic reflex (to a nettle sting) from the nettle stimulus to the response.
(20 marks)
The nettle sting (stimulus) is detected by pain Receptors in the hand.
These send impulses along a Sensory Neurone to a Relay Neurone in the CNS (the impulse is transmitted between the Neurones by neurotransmitters released into the synapse).
The impulse is then transmitted between the Relay Neurone and Motor Neurone.
Impulses travel along the Motor Neurone to the hand Muscles (the effector), which contract to move the hand away.
3 Main types of neuron:
3 marks
Sensory, Motor and Relay.
Reflex Action
11 marks
An automatic (involuntary) and rapid response to a stimulus, which minimises any damage to the body from potentially harmful conditions, such as touching something hot. They are therefore essential to the survival of many organisms.
They follow this general sequence and does not involve the conscious part of the brain. This is why the response is so fast.
What work together in a reflex action?
1 mark
Different types of Neurons.
Reflex Action Simplified
3 marks
Automatic and rapid response to a stimulus.
What is the Nerve Pathway followed by a reflex action called?
(1 mark)
a Reflex Arc
Example of a simple reflex arc
1 mark
Happens if we accidentally touch something hot.
Reflex Arc
4 marks
The pathway of information from a sensory neuron through an inter neuron to a motor neuron.
What are Organisms able to do to a Reflex Action?
4 marks
Modify and overcome it, but this uses the brain and has to be learnt.
Example of an Organism overcoming a Reflex Action
5 marks
Keeping hold of a hot object requires a nerve impulse to be sent to the motor neuron of the reflex arc to interfere with the normal reflex action to drop the object.
What type of Reproduction do humans use to produce offspring?
(3 marks)
Sexual Reproduction (the Genetic material in humans comes from a mother and a father).
True or false? A zygote is Haploid.
5 marks
False. A zygote is formed when a Male gamete fuses with a Female gamete, so it ends up with the full set of chromosomes (so is diploid).
Name the type of Cells that are formed when a Cell divides by meiosis.
How many of these are formed each time a Cell undergoes meiosis?
(2 marks)
Gametes are formed by meiosis. There are 4 gametes produced each time a Cell divides in this way.
How would the Genetic material in 1 Sperm Cell compare to the Genetic material in another Sperm Cell?
(5 marks)
The Genetic material will be different. (Chromosomes get shuffled during Meiosis and each Sperm Cell gets a random selection. So the Genetic material in each Sperm Cell is unique)
A mouse Body Cell contains 40 chromosomes.
How many chromosomes will be in the mouse cells produced by Meiosis.
(5 marks)
There will be 20 Chromosomes in each Cell (Gamete) after Meiosis. (Gametes are Haploid - they contain half the number of Chromosomes of a normal Cell)
Cats reproduce using Sexual Reproduction. What happens at the Cellular level during Sexual Reproduction in cats?
(9 marks)
A male and female cat each produce Gametes (Sperm + Eggs) by Meiosis. These contain half the number of Chromosomes of a normal Cell. An Egg from a female cat fuses with a Sperm from a male cat, forming a Zygote with the full number of Chromosomes.
What are the 4 different bases in DNA?
8 marks
DNA contains the bases Adenine (A), Thymine (T), Cytosine (C) and Guanine (G).
What is bigger - a Gene or a Genome?
6 marks
A Genome is bigger than a Gene. (The Genome is the entire DNA of an Organism. A Gene is a section of a DNA molecule that codes for a Specific Protein)
What is a Genome?
2 marks
Genome: The entire DNA of an Organism.
What is a Gene?
2 marks
Gene: A section of a DNA molecule that codes for a Specific Protein.
How many strands make up a section of DNA? What shape do they form?
(4 marks)
DNA is made up of 2 Polymer strands. These 2 strands coil together into a Double Helix.
Which bases in DNA pair together? What holds the base pairs together?
(5 marks)
A pairs with T
C pairs with G
The pairs are held together with weak Hydrogen Bonds.
Describe the structure of a Nucleotide.
5 marks
A Nucleotide consists of a Sugar, a Phosphate Group and 1 of the 4 different bases. The base is attached to the Sugar.
Sophia wants to extract DNA from some Strawberries.
Describe a method she could use.
(13 marks)
Mash the strawberries, put them in a beaker containing a solution of detergent and salt and mix them together.
Filter the mixture to get the froth and big, insoluble bits of Cells out.
Gently add some ice-cold alcohol to filter the mixture. Carefully fish out the stringy white precipitate (the DNA) with a glass rod.
Genome Cookbook Analogy
4 marks
Like a cookbook a Genome has many chapters (Chromosomes), which each have a set of recipes (Genes) telling you how to make anything from soup to cake (different Proteins).
What does Homozygous mean?
3 marks
Homozygous means you have 2 Alleles for a particular Gene that are the same.
True or False? Characteristics are rarely caused by multiple Genes interacting.
(3 marks)
False. Some Characteristics are caused by a single Gene, but most are caused by multiple Genes interacting.
What Alleles must you have to display a Recessive Characteristic?
(3 marks)
You must have 2 Recessive Alleles for a particular Gene.
Describe the difference between Genotype and Phenotype.
5 marks
Genotype is the combination of Alleles you have.
Phenotype is the Characteristics you have (which is determined by Alleles).
Describe a Genotype.
2 marks
A Genotype is the combination of Alleles you have.
What is a Phenotype?
2 marks
A Phenotype is the Characteristics you have, determined by Alleles.
A Punnett square shows the inheritance of Huntington’s Disease from 2 parents. Huntington’s Disease is caused by a dominant Allele. Is Parent 1 Heterozygous or Homozygous for Huntington’s Disease? What is their genotype?
Parent 1 - H h
Parent 2 - h h
(3 marks)
Parent 1 is Heterozygous - they have 2 different Alleles for the Huntington’s Gene. Their Genotype is Hh.
What is the ratio of affected (for Huntington’s Disease) offspring to unaffected offspring?
Parent 1 - Hh
Parent 2 - hh
(5 marks)
1:1
2 offspring are Heterozygous for Huntington’s - they have the Disease.
2 offspring are Homozygous recessive for Huntington’s - they don’t have the Disease.
The Alleles F and f are responsible for determining whether a person has Cystic Fibrosis. Cystic Fibrosis is caused by a Recessive Allele.
What is the probability of a child being born with Cystic Fibrosis if both parents have the Genotype Ff?
(3 marks)
There’s a 25% or 1 in 4 probability.
(Cystic Fibrosis is caused by a Recessive Allele, so the child will only have the disorder if they have the ff Genotype.)
How many pairs of Chromosomes are involved in determining Sex in humans?
(1 mark)
Only 1 pair of Chromosomes is involved in Sex determination.
What Chromosome(s) does each Sperm Cell contain?
A) X only
B) Y only
C) X and Y
D) either X or Y
(2 marks)
D
Each Sperm Cell will contain either an X Chromosome or a Y Chromosome.
What is the probability of inheriting an X Chromosome?
4 marks
There is a 100% chance of inheriting an X Chromosome. This is because you get 1 Chromosome from the Egg and 1 from the Sperm.
Since all eggs contain 1 X Chromosome, you will always inherit at least 1 X Chromosome.
Sex of offspring with XX Chromosomes
1 mark
Female
Chromosome found in Egg Cell
1 mark
1 X Chromosome
Sex of offspring with XY Chromosomes
1 mark
Male
Chromosome in Sperm Cell
1 mark
Either X or Y Chromosome
Si and Ava have 3 sons and 1 daughter. Si thinks there is a 75% chance that their next child will be a boy.
Explain whether or not Si is correct.
(3 marks)
Si is not correct. The probability that their next child will have XX Chromosomes is equal to the probability of the child having XY Chromosomes. So there’s 50% chance that their next child will be a boy.
A Family Pedigree shows how a family is affected by Tay-Sachs Disease. The Disease is caused by a Recessive Allele.
Is it possible for Baby X to be an unaffected non-carrier if the Mum is an affected Carrier and the Dad has Tay-Sachs Disease?
(5 marks)
No, the dad has the Disease, meaning he must have 2 Recessive Alleles.
So Baby X will inherit at least 1 Recessive Allele from his parents and will either be an unaffected carrier or have the Disease.
Is the Variation in Eye Colour in humans due to Genetic or Environmental Variation?
(1 mark)
Variation in Eye Colour is due to Genetic Variation.
How do mutations introduce Genetic Variation into populations?
(5 marks)
Mutations change the sequence of bases in DNA, which can result in an Allele (a different version of a gene) when they occur in a gene.
Describe how Sexual Reproduction causes Genetic Variation.
2 marks
Sexual Reproduction results in Alleles being combined in lots of different ways in offspring.
When a mutation occurs, what is the most common outcome of the Phenotype?
(4 marks)
Most mutations are neutral - they have no effect on the Phenotype. (Some mutations have a small influence on the Phenotype and, very rarely, a mutation will have a big effect on the Phenotype.)
Tom and Dom are identical twins. Dom weighs more than Tom. Tom has a scar on his back but Dom does not.
Give the type of Variation that caused these differences between Tom and Dom.
(2 marks)
Identical twins are genetically identical, so both of these differences must be caused by environmental variation.
In a field of sunflowers, there is variation in plant height.
Explain why you would expect to see this variation and what might cause it.
(6 marks)
E.g there is usually extensive Genetic Variation within a population of a species, mostly caused by mutations. This affects how tall each plant can grow.
There will also be variation caused by environmental factors, such as how much sunlight each plant gets.
Describe a Lower power Objective Lens.
4 marks
- Lens closest to specimen = short focal length and produces magnified image of specimen.
- In a Compound Microscope.
What is the Field of View?
1 mark
Area seen when looking through a microscope.
Once cells are in the middle of the field of view - you should?
(2 marks)
- Rotate a higher powered lens into place
- and begin to view the cells in more detail
What type of lens can become damaged as it’s close to the slide?
(1 mark)
High-powered Lens
