Unit 2 Flashcards
What is mitosis used for?
Growth and repair of cells.
How many copies of each chromosome do body cells have?
2
What does a body cell when it divides need to do?
Make new cells identical to the original cell.
Define mitosis.
Mitosis is when a cell reproduces itself by splitting to form two identical offspring.
What is the DNa like in a cell that’s not dividing?
It is all spread out in long strings.
What does it mean if a cell gets a signal to divide?
Needs to duplicate DNA.
What happens when DNA is duplicated?
It forms X shape chromosomes and each arm is a duplicate of the other.
What happens after DNa is duplicated in mitosis?
Chromosomes line up at the centre of the cell and cell fibres pull them apart. Two arms of each chromosome goes to opposite ends of the cell.
What happens after the arms of each chromosome goes to opposite sides of the cell in mitosis?
Membranes form around each of the sets which become the nuclei of the two new cells.
What is the final stage in mitosis?
The cytoplasm divides leaving two cells containing the same DNA and are identical.
Name an example of an organism that reproduces using mitosis.
Strawberry plants which form runners which turn into new plants. This means the offspring have exactly the same genes as the parent with no genetic variation.
When do scientists believe life began?
3-4 billions of years ago.
What are some of the best evidence from history of life?
Fossils.
Define fossils.
Remains of organisms from many thousands of years ago or millions that are found preserved in ice, rocks and other places.
How are fossils formed?
When an animal/plant does not decay after death, when parts of an animal are replaced by minerals, from traces of animals such as footprints and from the hard parts of an animal.
Why might an animal or plant not decay after death?
One or more conditions for decay are not present such as enough oxygen, temperature may be too low and poisonous gases may have killed off bacteria that cause decay.
What happens when an animal or plant does not decay after death?
Preserved in ice then scientists can extract DNA and compare it to modern organisms.
What are the most common fossils?
Hard parts of animal or plant are replaced with minerals.
Why is there an incomplete record of fossils?
Many of the earlier life forms were soft bodied organisms so little fossil trace. This is why there is little evidence of how life began.
Why did most organisms not become fossilised?
Right conditions for fossil formation were rare.
How was some fossils formed in rocks destroyed?
By geological activity, broken down, worn away, melted or buried.
What are the stages of fossil formation?
The reptile dies and falls to the ground
The flesh rots leaving the skeleton to be covered in sand soil or clay before damage
Skeleton becomes mineralised and turns to rock. Rocks shift in earth with fossil trapped inside
Eventually the fossil emerges as the rocks move and erosion happens
What do the fossil records help us to understand?
How much organisms have changed since life developed on Earth.
Why is the understanding limited of how organisms have changed since life developed?
Because only small bits of skeletons or little bits of shells have been found.
Which animals have not appeared to change very much?
Fossils sharks evolved early into a form that was almost perfectly adapted for environment and life and their environment has not changed much.
How many species do scientists estimate to have existed?
4 billion although only a few million exist today.
What was the horse like from 55 million years ago?
Small, swamp dwelling with well spread toes for walking on soft ground.
What was the horse like from 25 million years ago?
Bigger, walking on one enlarged toe for speed.
What is the modern horse like?
Fast runner on hard ground- only one toe forming the hoof.
Define extinction.
Permanent loss of all the members of a species.
Why do some species become extinct?
Conditions change and new species evolve that are better suited to survive. Old species cannot cope with changes and gradually die out because not able to compete so well for food and other resources.
What has happened to the species that have died out?
Lost forever or only exist in fossil records. Others have left living relatives.
How do plants and algae make food?
By photosynthesis.
Where does photosynthesis take place?
Green parts of plants when it is light.
What is the word equation for photosynthesis?
Carbon dioxide + water + light energy- glucose + oxygen.
What are cells in algae and leaves of a plant full of?
Small green parts known as chloroplasts.
What do chloroplasts contain?
Chlorophyll.
Define chlorophyll.
A green pigment, found in plants, which are responsible for the absorption of light to provide energy for photosynthesis.
What are the stages of photosynthesis?
Light energy is absorbed by chlorophyll in chloroplasts.
This energy is used to convert carbon dioxide and water from the soil into glucose.
It also produces oxygen as a by product which is released into the air which we can use to breathe.
Some glucose is immediately used by the cells but lots of it is converted into insoluable starch and stored.
What are the two ways you can test to see if photosynthesis is occurring?
Producing oxygen method or using iodine solution.
How can you use iodine solution to test for starch?
Iodine solution is a yellowy brown liquid which turns dark blue when it reacts with starch.
What is the method of using iodine solution to test for starch?
Take a leaf from a plant that has been kept in the light and one in dark for 24 hours.
Treat the leaves by boiling them in ethanol.
Rinse leaves in hot water.
Add iodine solution.
Why do you need to boil leaves in ethanol in testing for starch using iodine?
To destroy the waxy (waterproof) cuticle which keeps the iodine out so it cannot react with starch and remove the colour.
Why do you need to rinse the leaves in hot water?
To soften them.
What are variegated leaves?
They have green parts (with chlorophyll) and white parts (without chlorophyll).
What happens to leaves kept in the dark after iodine solution is added?
Turn white, showing there is no starch and showing the importance of light in photosynthesis.
How can you show a plant is photosynthesis by showing it produces oxygen?
Use water plants you can see and collect the bubbles of gas they give off. The gas will relight a glowing splint showing it is oxygen.
Where does aerobic respiration take place?
In the mitochondria of cells.
Why do mitochondria have a folded inner membrane?
To provide a large surface area for enzymes involved in aerobic respiration.
How can you tell how active a cell is?
By how many mitochondria there are in the cell.
Give the word equation for aerobic respiration.
Glucose + oxygen- carbon dioxide + water (+energy)
Why is aerobic respiration important?
Releases energy for cells to use to carry out basic functions of life.
What works to provide cells with glucose and oxygen?
Digestive system, lungs and circulation.
How can you show cellular respiration is taking place?
You can identify carbon dioxide as a waste product by showing how limewater goes cloudy when carbon dioxide bubbles through it.
What will make the limewater go cloudier quickly when testing for cellular respiration?
The higher the concentration of carbon dioxide.
What would a rise in temperature show for cellular respiration?
Shows energy is being released.
Why do we use aerobic respiration?
Mammals and birds use it to keep bodies at constant temperature inside regardless of surroundings.
Animals use it for contracting muscles.
Build up larger molecules from smaller ones to make new cell material ie sugars and nitrates built up into amino acids. These are then built up into proteins.
What shape are mitochondria?
Tiny rod shaped parts (organelles)
Why do muscle cells have many mitochondria but fat cells very few?
Muscle cells are used for movement which requires lots of energy through aerobic respiration so many mitochondria are needed. Fat cells are for storage not releasing energy so they do not have as much.
What is the heart made of and what does it do?
Made of muscle and pumps blood around your body.
What is muscle tissue made up of?
Protein fibres.
In what situation do muscles contract?
When supplied with energy from respiration. They need a lot of energy.
What do muscle tissue contain?
Many mitochondria to carry out aerobic respiration and supply energy.
What do muscle fibres usually occur in?
Big groups known as muscles which contract to cause movement then relax to allow others to work.
What do muscles store glucose as?
The carbohydrate glycogen which can be rapidly converted back to glucose to use during exercise.
What happens when muscular activity increases in the body?
Heart rate increases and arteries supplying blood to muscles dilate.
Increases blood flow to exercising muscles
Increases supply of oxygen and glucose
Increases rate of co2 removed from muscles
Breathing rate increases and breathe more deeply
Breathe more often and bring in more oxygen which is picked up by red blood cells which carries it to exercising muscles
More co2 can be removed from blood in lungs and breathed out
What are the benefits of exercise?
Your heart and lungs become larger meaning they develop a bigger and more efficient blood supply so they function as efficiently as possible.
What happens when you exercise to your muscles?
Contract harder and faster so need more energy and glucose and oxygen for energy needs. Produce increased amounts of CO2 which needs to be removed to keep them working effectively.
What are protein molecules made up of?
Long chains of amino acids.
What do different arrangements of amino acids give you?
Different properties.
Name some functions of proteins.
Structural components ie. Muscles and tendons.
Hormones ie. Insulin
Antibodies to destroy pathogens
Catalysts such as enzymes.
What is a catalyst?
A substance that speeds up a reaction but doesn’t get used up.
What are enzymes?
Large protein molecules made up of long chains of amino acids that are folded to produce a molecule with a specific shape and act as biological catalysts.
What does the special shape of an enzyme allow it to do?
Other molecules (substrates) to fit into the enzyme protein.
What are enzymes involved in?
Building large molecules from lots of smaller ones, changing one molecule into another, breaking down large molecules into smaller ones.
Give an example of an enzyme building large molecules from lots of smaller ones.
Glycogen can be built to create glucose, amino acids and proteins.
Give an example of an enzyme changing molecules into another (one sugar into another etc)
Glucose into fructose.
Give an example of an enzyme breaking down bigger molecules into smaller ones.
Insoluable food material into small soluable materials ie glucose.
How do enzymes work?
The substrate (reactant) of the reaction fits into the active site (shake) of the enzyme. They then bind together and reaction takes place and products are released from the surface of the enzyme.
Define enzyme.
A biological catalyst made of protein.
Define active site.
The special part in the structure of an enzyme where the substrate binds.
Define protein.
A large molecule composed of one or more long chains of amino acids.
What does DNA stand for?
Deoxyribonucleic acid.
Where is DNA found?
Nucleus in really long molecules called chromosomes.
What does DNA contain?
All the instructions to put an organism together and make it work.
What is a gene?
Section of DNA that contains the instructions to make a specific protein.
How do cells make proteins?
By putting amino acids in a particular order.
What do genes tell us?
What order to put amino acids in.
What does DNA also determine?
What protein the cell produces ie keratin which also determines what type of cell it is eg. Skin cell.
What is DNA fingerprinting?
Way of cutting up a persons DNA into small sections then separating them.
