OCR GCSE Biology

What is the equation for anaerobic respiration in plants and fungi?

What is the equation for anaerobic respiration in plants and fungi?

Glucose --> Ethanol + Carbon Dioxide.

What is the word equation for anaerobic respiration in animals?

Glucose --> Lactic Acid

What is anaerobic respiration?

'Anaerobic' means "without oxygen".

What is the equation for aerobic respiration?

Glucose + Oxygen --> Carbon Dioxide + Water

What is aerobic respiration?

Aerobic respiration is what happens when there's plenty of oxygen available. It is the most efficient way to transfer energy from glucose.

How can cells respire?

Cells can respire using glucose as a substrate, but organisms can also break down other organic molecules (e.g carbohydrates, proteins and lipids) to use as substrates for respiration.

How is respiration controlled?

Respiration is controlled by enzymes.

What can effect the rate of respiration?

The rate of respiration can be effected by temperature and pH.

What type of reaction is respiration?

Exothermic (because it transfers energy to the surroundings).

How does substrate concentration effect the rate of reaction?

The higher the substrate concentration, the faster the reaction but only to a certain extent.

How does enzyme concentration effect the rate of reaction?

Increasing the concentration of the enzyme increases the rate of reaction but in some cases there are more than enough enzyme molecules to deal with the available substrate, so adding more enzymes would have no further effect.

How does pH effect enzymes?

If the pH is too high or too low, it interferes with the bonds holding the enzyme together which changes the shape of its active state- causing it to denature.

What is the optimum pH for enzymes?

The optimum pH is often 7 but not always, e.g pepsin is an enzyme used to break down proteins in the stomach and it works best at a pH of 2.

What is an enzymes optimum temperature?

37 degrees (body temperature).

How does temperature effect enzymes?

A higher temperature increases the rate at first.

What happens if an enzyme loses its shape?

It cannot catalyse the reaction.

How are enzymes specific?

They have an active site where it joins on to its substrate. They all have their own specific substrate.

What happens if an enzyme's active site does not match the substrate?

The reaction will not be catalysed.

What is the term used to describe an enzyme's active site bonding to its substrate?

Lock and Key hypothesis.

What are enzymes mainly used for?

They are usually used as biological catalysts as they reduce the need for high temperatures and they speed up chemical reactions in the body.

What happens in protein synthesis?

In the nucleus, the two DNA strands unzip around the gene. The DNA is used as a template to make mRNA. Base pairing ensures it is complementary. This is transcription. The mRNA molecule moves of of the nucleus into the cytoplasm. Amino acids that match the triplet codes on mRNA join together. This makes the protein coded for by the gene. This is called translation.

What is transcription?

Transcription is the process by which the information in a strand of DNA is copied into a new molecule of messenger RNA (mRNA).

What is translation?

Translation is a step in protein biosynthesis wherein the genetic code carried by mRNA is decoded to produce the specific sequence of amino acids in a polypeptide chain.

Where are proteins synthesised?

Proteins are synthesised in the cytoplasm.

What are proteins made?

Proteins are made from chains of molecules called amino acid. Each protein has its own specific number and order of amino acids.

What is a polymer?

A polymer is a large complex molecule composed of long chains of monomers joined together.

What is a monomer?

Monomers are small, basic molecular units.

What do nucleotides contain?

Sugar and phosphate. The base of a each nucleotide is the only part of the molecule that varies. The base is attached to the sugar.

What are the complementary base pairs?

A(denine) <b>pairs with</b> T(hymine)
C(ytosine) <b>pairs with</b> G(uanine)

What shape is DNA?

A double helix.

What are the two DNA strand made up of?

The two DNA strands are made up of nucleotides joined together in a long chain called polymers.

What do animal cells contain?

Nucleus, Cytoplasm, Mitochondria, Cell Membrane

What is the function of a nucleus?

It contains DNA and controls the cell's activity.

What is the function of cytoplasm?

Cytoplasm is a gel like substance where chemical reactions occur.

What is the function of the mitochondria?

It is the site of cellular respiration and it contains enzymes which are needed for chemical reactions.

What is the function of the cell membrane?

It holds the cell together and controls what goes in and out of the cell by providing a selective barrier. They contain receptor molecules that are used for cell communication.

What is a prokaryote?

Prokaryotes are smaller and simpler cells.

What is a eukaryote?

Eukaryotes are complex cells.

What is the equation for magnification?

Magnification=image size/real size.

What are chromosomes?

Chromosomes are long molecules of coiled up DNA. The DNA is divided up into short sections called genes.

What do bacterial cells contain?

Chromosomal DNA, Plasmids and a Cell Membrane.

What is the function of chromosomal DNA?

It is one long circular chromosome which controls the cells activities and replication. It floats in the cytoplasm.

What is the function of a plasmid?

A plasmid is a small loop of extra DNA that is not a part of the chromosome. Plasmids contain genes for things like drug resistance and it can be passed on between bacteria.

What do plant cells have that animal cells do not?

Cell wall, chloroplasts.

What is the function of the cell wall?

It provides support and it is made up of cellulose.

What are the functions of chloroplasts?

They carry out photosynthesis (it's where it occurs) and they contain chlorophyll.

What is the cell cycle?

It is when cells in the body divide to produce more cells, so your body can grow and replace damaged cells and cells grow and divide over and over again.

Define mitosis.

Mitosis is when a cell reproduces itself by splitting to form two identical offspring.

What is the first stage of mitosis?

The cell has two copies of its DNA all spread out in long strings.

What is the second stage of mitosis?

The DNA forms X-shaped chromosomes. Each 'arm' of a chromosome is an exact copy of the other. This happens before the cell divides.

What is the third stage of mitosis?

The chromosomes then line up at the center of the cell and cell fibers pull them apart. The two arms of each chromosome go to opposite ends of the cell.

What is the fourth stage of mitosis?

Membranes from around each of the sets of chromosomes. these become nuclei of the two new cells.

What is the fifth and final stage of mitosis?

The cytoplasm divides; two new cells containing exactly the same DNA as they're genetically identical to each other and to the parent cell.

What is differentiation?

Differentiation is the process by which a cell changes to become specialised for its job.

What is an example of differentiation in plants?

Palisade leaf cells carry out photosynthesis as they contain chloroplasts. Their tall shape means that they have a lot of surface area exposed down the side for absorbing carbon dioxide from the air in the leaf, and their thin shape means that you can fit loads of them in at the top of a leaf, so they're nearer the light.

What is an example of differentiation in animals and humans?

A sperm's function is to get the male DNA to the female DNA during reproduction. Sperm have long tails and streamlined heads to help them swim, they contain lots of mitochondria to provide them with energy and they have enzymes in their heads to digest through the egg's cell membrane.

What do specialised cells in multicellular organisms do in order to carry out their function?

In multicellular organisms, specialised cells are grouped together to form tissues- groups of cells working together to perform a particular function. Different tissues work together to form organs. Different organs make up an organ system.

What is an example of an undifferentiated cell?

Stem cells are undifferentiated but depending on what instructions they're given, they can divide by mitosis to become new cells, which then differentiate.

Why are embryonic stem cells so important for growth and repair?

They have the potential to become any kind of cell.

Where can you find stem cells in the body?

In adults, stem cells can be found in bone marrow. You can also find them in the umbilical cord.

What is the main disadvantage of stem cells?

They cannot turn into any type of cell.

What are the only cells in plants that divide by mitosis?

Meristems- they are found in plant tissues.

Where is meristem tissue found in the plant?

Anywhere in the plant thats growing- e.g the roots and shoots.

What type of cells do meristems produce?

They produce unspecialised cells that are able to divide into any cell type in the plant and they act like embryonic stem cells.

What can the unspecialised cells in the plant become?

They can become specialised and form tissues like xylem and phloem.

What is diffusion?

Diffusion is the net (overall) movement of particles from an area of higher concentration to an area of lower concentration.

In what states can diffusion occur?

Liquids and gases as the particles are free to move around.

What type of molecules can diffuse through the cell membrane?

Very small molecules like glucose, amino acids, water and oxygen.

What is the first step of diffusion?

Particles move through the cell membrane from where there is a higher concentration to where there is a lower concentration and they are moving in random motion.

What is active transport?

Active transport is the movement of particles across a membrane against a concentration gradient from an area of lower concentration to an area of higher concentration using ATP released during respiration.

How does active transport work in the digestive system?

When there is a higher concentration of nutrients in the gut they diffuse into the blood but sometimes there is a lower concentration of nutrients in the gut than in the blood. Active transport allows nutrients to be taken into the blood, despite the concentration gradient being the wrong way. This stops us from starving.

What does active transport need in order to take place?

ATP from respiration.

What is osmosis?

Osmosis is the net 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 a partially permeable membrane?

A partially permeable membrane is a membrane with very small holes in it. Only tiny molecules, like water, can pass through them. A cell membrane is a partially permeable membrane.

What direction do water molecules pass through the membrane? Why does this happen?

They pass both ways through the membrane during osmosis because water molecules move randomly all the time.

What is water potential?

Water potential is the likelihood of water molecules to diffuse out of or into a solution. If a solution has a high water potential, it has a high concentration of water molecules and vice versa.

What does it mean if a plant is turgid?

Plump and swollen due to the increased water potential in the soil when you water a plant.

What is turgor pressure?

When the contents of the cell push against the cell wall. this helps support the plant tissues.

What does it mean if a plant is flaccid?

The plant will wilt as it starts to lose water. however, the plant does not lose its shape because the inelastic cell wall keeps things in position.

What happens to animal cells when they are surrounded by a solution with a high water potential?

The cells can burst as they do not have a cell wall.

What factors effect the movement of substances?

What happens to proteins in the body, as they cannot be stored?

Any excess amino acids are converted in the liver into fats and carbohydrates, which can be stored.

What is the waste product formed from converting excess amino acids?

Urea- it is poisonous and is removed from the blood by the kidneys and removed from the body in the urine.

How do single-celled organisms exchange substances?

They are only one cell big, so substances can diffuse straight into and out of single-celled organisms across the cell membrane. The substances only have to travel a short distance and they have a large surface area to volume ratio.

Why is it difficult for multicellular organisms to exchange substances?

Some cells are deep inside the organism- it's a long way for the substances to travel and they have a low surface area to volume ratio which means their outer surface is small.

How are the exchange surfaces in specialised exchange organs adapted to maximise effectiveness?

>They are thin, sos substances have a short distance to travel.
>They have a large surface area, so lots of substance can move at once.
>Exchange surfaces in animals have lots of blood vessels to get things into and out of the blood quickly.
>Gas exchange surfaces in animals are often ventilated (air moves in and out).

Where does gas exchange happen in the lungs?

The lungs contain millions of little air sacs called alveoli where gas exchange takes place.

How are alveoli specialised to maximise diffusion?

>An enormous surface area.
>Thin walls.
>A moist lining for dissolving gasses.
A good blood supply.

What happens to the blood passing next to the alveoli?

It returns to the lungs from the rest of the body via the hear so it contains lots of carbon dioxide and very little oxygen.

What happens to carbon dioxide during gas exchange in the lungs?

Carbon dioxide diffuses out of the blood (with a higher concentration) into the alveolus (a lower concentration) to be breathed out.

What happens to oxygen during gas exchange in the lungs?

Oxygen diffuses out of the alveolus (higher concentration) into the blood (lower concentration).

Where are dissolved food molecules absorbed out of the digestive system?

The small intestine is where dissolved food molecules are absorbed out of the digestive system and into the blood.

What is the small intestine covered with?

Tiny little projections called villi.

What is the role of villi?

They increase the surface area in a big way so that dissolved food molecules are absorbed much more quickly into the blood. They have a single layer of surface cells and a very good blood supply to assist quick absorption.

How are leaves specialised to maximise the diffusion of oxygen and carbon dioxide?

>Leaves are broad, so there is a large surface area.
>They are also thin, which means gases only have to travel a short distance.
>There are air spaces inside the leave which lets gases move easily between cells.
>The lower surface is full of little holes called stomata. They let the gases diffuse in and out and they also allow water escape (transpiration).

How are root hairs important for absorbing water and mineral ions?

The cells on a plant roots grow into long 'hairs' which stick out into the soil and each branch of a root will be covered in millions of microscopic hairs. This gives the plant a big surface area for absorbing water and mineral ions.

What happens when root hairs take in water and mineral ions?

There is a higher concentration of water in the soil than there is inside the plant, so the water is drawn into the root hair cell by osmosis. Mineral ions move in by active transport, since the concentration of mineral ions in the root hair cells is usually higher than the soil.

What is the double circulatory system made up of?

The heart, blood vessels and blood. Because it is a double circulatory system, there are two circuits joined together.

What happens in the first circulatory circuit?

The heart pumps deoxygenated blood to the gas exchange surfaces in the lungs to take in oxygen. The oxygenated blood then returns to the heart.

What happens in the second circulatory circuit?

The heart pumps oxygenated blood around all the other organs of the body. The blood gives up its oxygen at the body cells and the deoxygenated blood returns to the heart to be pumped out to the lungs again.