OCR Biology A level

What is the MAIN role of membranes and what are the other roles?

-COMPARTMENTALISATION

-site of chemical reactions

-cell signalling

-cell adhesion

How do cell membranes compartmentalise?

Membranes are hydrophobic layers that separate different regions of substances dissolved in water. This hydrophobic layer acts as a barrier preventing the movement of hydrophilic molecules from one region to another. It keeps one compartment separate from another.

What are the 3 examples of membrane compartmentalisation?

-separate contents of the cell from the environment

-separate different areas of the cell from each other (organelles)

-separate different areas within organelles

How are cell membranes sites of chemical reactions?

Some enzymes or electron carriers involved in aerobic respiration or photosynthesis have to be in particular positions relative to each other in order to work. Being membrane bound allows these organelles to be maintained.

What is cell signalling and how are cell membranes involved in cell signalling?

Cell signalling is where one cell releases a chemical which causes a response in another cell. Glycoproteins are often the receptors on cells that detect the presence of the chemical and cause changes to the cell.

What is cell adhesion and how are cell membranes involved in cell adhesion?

The binding of a cell to a particular surface or substrate particularly the extracellular matrix of another cell. Some types of glycoproteins perform this role.

What are the 5 components of membranes?

-phospholipids

-glycolipids

-proteins

-glycoproteins

-cholesterol

Fill in the blanks:

Membranes are a ______ ______. The membrane is ______ layers of ______ that is about ______ nm thick in total. Each layer has the hydrophilic ______ ______ of the ______ pointing out of the membrane and the hydrophobic ______ pointing into the centre of the membrane.

Membranes are a PHOSPHOLIPID BILAYER. The membrane is TWO layers of PHOSPHOLIPIDS that is about 7 nm thick in total. Each layer has the hydrophilic PHOSPHATE HEADS of the PHOSPHOLIPID pointing out of the membrane and the hydrophobic TAILS pointing into the centre of the membrane.

Explain the fluid mosaic model of membrane structure.

The term fluid refers to the fact that the phospholipids are free to move with the layer relative to each other. The term mosaic refers to the fact that proteins of various shapes and sizes are embedded in the membrane resembling a patchwork.

What is a membrane protien?

Proteins embedded within membranes. They can be intrinsic or extrinsic proteins depending on the way they are associated with the membrane.

What are intrinsic proteins?

Transmembrane proteins are embedded through both layers of the membrane.

What are 3 examples of intrinsic proteins.

-Channel proteins

-Carrier proteins

-Glycoproteins

What are extrinsic proteins?

Peripheral proteins are present in one side of the membrane.

What are 2 examples of extrinsic proteins?

-Enzymes

-Proteins that bind cytoskeleton to membrane

What is the function of channel proteins?

Intrinsic proteins that allow the passive movement of polar molecules down their concentration gradient each channel is specific for a specific molecule or ion. The molecule provides a hydrophilic channel through the membrane.

What is the function of carrier proteins?

Intrinsic proteins that allow either passive or active movement of polar molecules or ions down their concentration gradient or the active transport of polar or ions against their concentration gradient. Transport involves the shape of the protein changing.

What are glycoproteins and what are their functions?

Proteins with attached carbohydrate chains of varying lengths and shapes. They play a role in cell adhesion as well as receptors for chemical signals.

What are receptors and what are their functions?

Usually glycoproteins, they detect the presence of an extra cellular chemical that causes a response in the cell.

What are glycolipids and what are their functions?

Lipids with an attached carbohydrates chain. They are cell markers or antigens ad are involved in the recognition of self and non self by immune system.

What are 3 polysaccharides that are storage molecules and how are they suited for this?

Amylose, amylopectin and glycogen

What are phospholipids?

the molecule that allow the membrane to hold its form and generate a hydrophobic barrier between one side of the membrane an the other

What are the two main types of cells and what is the difference between them?

Eukaryotic cells (have a nucleus and membrane bound organelles) and Prokaryotic cells (without a nucleus or membrane bound organelles)

What does cell ultrastructure describe?

The structures that cells are made of.

State whether cell walls are present in animals/plants/both, describe the structure and the function.

Cell wall are present in plants only

Cell walls are a layer of cellulose(chitin in fungi) outside the plasma membrane that may have holes in that join to adjacent cells called plasmodesmata.

It allows the cell to become turgid by preventing bursting. It is freely permeable. Plasmodesmata allow the movement of substances between cells.

State whether centrioles/centrosomes are present in animals/plants/both, describe the structure and the function.

Centrioles/ centrosomes are present in animals only.

The centrosome consists of two centrioles perpendicular to each other. Each centriole is a tube made from microtubules.

It is involved in the assembly and organisation of microtubules (particularly the spindle fibres) during cell division.

State whether chloroplasts are present in animals/plants/both, describe the structure and the function.

Chloroplasts are present in plants only.

It's structured consists of a double membrane layer around the outside with an internal membrane system suspended in gel called stroma.

It is the site of photosynthesis.

State whether cytoplasm is present in animals/plants/both, describe the structure and the function.

Cytoplasm is present in animals and plants.

it is the gel within the plasma membrane.

The site of all reactions not performed in an organelle. Organelles are suspended in the cytoplasm and molecules can pass through it.

State whether cytoskeleton is present in animals/plants/both, describe the structure and the function.

Cytoskeleton is present in both animals and plants.

It is a network or 3 types of protein fibres (microtubules, microfilaments and intermediate fibres.)

It stabilises cell shape. Allows organelles to be moved about the cell. Allows some cells to move, Coordinates the movement of chromosomes in cell division.

State whether flagella and cilia are present in animals/plants/both, describe the structure and the function.

Flagella and cilia are present in animals only.

finger-like projections of the plasma membrane containing cytoplasm and a 9+2 arrangement of microtubules.

The move to either move the cell (flagella) or substances over the surface of the cell (cilia).

State whether Golgi apparatus/ body are present in animals/plants/both, describe the structure and the function.

Golgi apparatus are present in plants and animals.

They are a collection of flattened sacs called cisternae made of membrane with an inner space called the lumen.

It modifies proteins and packages them in vesicles for transport around the cell or secretion out of it.

State whether large permanent vacuole is present in animals/plants/both, describe the structure and the function.

Large permanent vacuoles are present in plants only.

It is a large membrane bound sac. Surrounded by a membrane called tonoplast and containing sap.

It stores water, ions, waste products and a range of other molecules. It swells due to water entering it and causes the cell to become turgid.

State whether lysosomes are present in animals/plants/both, describe the structure and the function.

Lysosomes are present in both animals and plants.

It is a membrane-bound sac that contains hydrolytic enzymes.

It is used for breaking down faulty organelles or engulfed bacteria. Also used in autolysis (programmed cell death).

State whether microvilli are present in animals/plants/both, describe the structure and the function.

Microvilli are present in animals only.

They are finger-like projections of the plasma membrane.

It increases the surface area of the cell for better absorption.

State whether mitochondria are present in animals/plants/both, describe the structure and the function.

Mitochondria are present in both plants and animals.

It has a double membrane layer around a gel called matrix. The inner membrane is heavily folded.

It is the site of aerobic respiration to generate ATP for cell functions.

State whether a nuclear envelope is present in animals/plants/both, describe the structure and the function.

The nuclear envelope is present in both animal and plant cells.

It is a double membrane layer containing holes called nuclear pores that surrounds the nucleus.

The membrane is continuous with the endoplasmic reticulum.

It allows the entry or exit of molecules into or out of the nucleus.

State whether nucleolus are present in animals/plants/both, describe the structure and the function.

Nucleolus are present in both animals and plants.

It is a dark staining region of the nucleus that isn't membrane bound, it contains a high density of nucleic acids.

It is the site of ribosome production.

State whether a nucleus is present in animals/plants/both, describe the structure and the function.

Nucleus are present in both animals and plants.

It contains DNA as linear chromosomes and is surrounded by the nuclear envelope.

It coordinates the functions of the cell.

State whether plasma/cell surface membranes are present in animals/plants/both, describe the structure and the function.

Plasma/ cell surface membranes ae present in both animals and plants.

It is a double layer of phospholipids with proteins and cholesterol embedded within it.

It allows control of what enters and leaves the cell.

State whether ribosomes are present in animals/plants/both, describe the structure and the function.

Ribosomes are present in both animals and plants.

They are made of protein and RNA, not membrane bound and can be free in the cytoplasm or bound to RER.

It is the site of protein synthesis.

State whether amyloplast are present in animals/plants/both, describe the structure and the function.

Amyloplast are present in plants only.

They are membrane bound sacs containing starch.

They act as a starch store for plants.

State whether a rough endoplasmic reticulum is present in animals/plants/both, describe the structure and the function.

RER are present in both plants and animals.

They are a network of tubes or sacs called cisternae surrounded by a membrane. The membrane has ribosomes attached to is external surface.

Proteins fold into shape inside the RER before they are packaged into transport vesicles.

State whether a smooth endoplasmic reticulum is present in animals/plants/both, describe the structure and the function.

The SER is present in both plants and animals.

It is a network of tubes or sacs called cisternae surrounded by a membrane.

It is the site of lipid and carbohydrate synthesis.

State whether vesicle (transport or secretory) are present in animals/plants/both, describe the structure and the function.

Vesicles are present in both plants and animals.

They are small spheres enclosed by a membrane. they contain a variety of molecules dependant on their function.

They transport molecules from one organelle to another or out of the cell.

What are 4 details about the mitochondrial structure.

Two membranes surround the matrix

The inner membrane is heavily folded and contains ATP synthase (the site of ATP synthesis)

The folds are called cristae

Contains 70S ribosomes and circular DNA

What are 5 details about the chloroplast structure?

Two membranes surround the stroma.

A third membrane system within the stroma has flattened sacs called thylakoids, arranged in stacks called grana.

The thylakoid membrane contains chlorophyll.

Contains 70S ribosomes and circular DNA

Contains starch granules and lipid droplets.

What is protein trafficking?

How proteins are produced and transported.

What are the 5 steps of protein trafficking?

1) proteins are synthesised on the ribosomes bound to the endoplasmic reticulum

2) They pass into the cisternae and are packaged into transport vesicles

3)Vesicles containing newly synthesised proteins move towards the Golgi apparatus.

4) the vesicle fuses with the Golgi apparatus and proteins enter, the proteins are modified before leaving the Golgi apparatus in vesicles.

5) Secretory vesicles carry proteins that are to released cell. The vesicle move towards and fuse with the cell surface membrane, releasing its contents by exocytosis.

Describe microfilaments and its function?

Contractile fibres formed from the protein actin.

These are responsible for cell movement and also cell contraction during cytokinesis.

Describe intermediate filaments its function?

Fibres

That give mechanical strength to cells to help maintain their integrity.

Describe microtubules its function?

Globular tubulin proteins polymerise to form tubes.

These are used to form a scaffold like structure that determines the shape of the cell. They also act as tracks for movement of organelles(including vesicles) around the cell. They also make spindle fibres that separate chromosomes in cell division.

What type of organisms are eukaryotic and what types are prokaryotic?

Eukaryotic organisms are multi cell whereas prokaryotic organisms are unicellular (single celled)

What size are eukaryotic cells and what size are prokaryotic cells?

Eukaryotic cells are 20-40 um whereas prokaryotic cells are 0.5-5 um

Is a nucleus present/absent in eukaryotic and prokaryotic cells?

Eukaryotic cells have a nucleus whereas prokaryotic cells don't have a nucleus.

What is the location of genetic material in eukaryotic and prokaryotic cells?

In eukaryotic cells, genetic material is located in the nucleus whereas genetic material is free in the cytoplasm of prokaryotic cells.

What is the difference between ribosomes in eukaryotic and prokaryotic cells?

Ribosomes in eukaryotic cells are larger at 80S (22nm) whereas ribosomes in prokaryotic cells are smaller at 70S (18nm).

Are organelles present in eukaryotic cells and prokaryotic cells?

Organelles are present in eukaryotic cells however are not present in prokaryotic cells.

What are eukaryotic cell walls made of and what are prokaryotic cell walls made of?

Eukaryotic cell walls are made from cellulose (chitin in fungi) whereas prokaryotic cell walls are made from peptidoglycan.

What is the difference between flagellum in eukaryotic and prokaryotic cells.

In eukaryotic cells, flagellum are made from a 9+2 arrangement of microtubules whereas the structure is different in prokaryotic cells.

Compare reproduction in eukaryotic and prokaryotic cells?

Eukaryotic cells reproduce asexually or sexually whereas prokaryotic cells reproduce through binary fission.

How would you test for reducing sugars and what would a positive test be?

For a reducing sugar test you would use Benedict's test for reducing sugars.

For this you:

-Ensure chemical is in solution

-Add Benedict's reagent

-Heat to 80C

A positive test would go from blue to brick red.

How would you test for non-reducing sugars and what would a positive test be?

For a non-reducing sugar test you would use Benedict's test for non-reducing sugars.

For this you:

-Do a reducing sugar test

-Then heat with acid

-Neutralise solution

-Add Benedict's reagent

A positive test would appear blue for the reducing sugar test then go from blue to brick red.

How would you test for starch and what would a positive test be?

For a starch test you would use the iodine test.

For this you:

-Add iodine

A positive test would change from orange-brown to blue-black

How would you test for lipids and what would a positive test be?

For a lipids test you would use the lipid emulsion test.

For this you:

-Add ethanol and shake

-Then add the mix to water

A positive test would go from colourless to a cloudy white emulsion.

How would you test for proteins and what would a positive test be?

For a protein test you would use a Biuret test.

For this you:

-Ensure chemical is in solution

-Add Biuret reagent

A positive test would go from pale blue to purple.

Explain with reference to electronegativity, why water is polar.

The presence of unevenly distributed charge on the molecules makes water polar. This is because the oxygen in the water has much higher electronegativity than hydrogen. This means that the electrons are closer to the oxygen that results in the oxygen having a slightly positive charge and hydrogen having a slightly negative charge.

What are hydrogen bonds?

A bond between 2 polar molecules (in this case Oxygen and Hydrogen of adjacent water molecules).

Why is water a good solvent, what does this mean and why is this important for living organisms(2).

It is polar because electrons aren't shared equally between O and H.

This means that it dissolves any charged molecule as it can H-bond with them.

This is useful as:

- it allows dissolved molecules to move around and allow reactions to occur.

-It also allows organisms to absorb molecules from the environment.

Why is water a liquid over a wide range of temperatures, what does this mean and why is this important for living organisms(3).

The melting point and boiling point are relatively far apart.

This is because the H-bonds hold water molecules to each other which raises the boiling point.

This is useful as:

- it is a good transport medium.

-It can be a habitat for organisms to easily move through

-It acts as a lubricant

Why does water exhibit adhesive and cohesive forces, what does this mean and why is this important for living organisms(1).

Water forms H-bonds with other polar/ charged molecules

This means that water bonds with each other (cohesion) and other molecules (adhesion)

This is useful for:

-transport in plants as that relies on the cohesion of water.

Why does water have a high specific heat capacity, what does this mean and why is this important for living organisms(2).

H-bonds require extra energy to break so less is available to increase the kinetic energy of the molecules.

This means that it takes lots of energy to raise the temperature of a certain volume by 1C.

This is useful as:

-It keeps the temperature inside cells/organisms relatively stable.

-It creates relatively thermostable environments.

Why is solid water less dense than liquid water, what does this mean and why is this important for living organisms(1).

H-bonds hold water further apart than when some are broken, in solid state there isn't enough energy to break H bonds so there are more.

This means that ice floats on top of bodies of water and insulates the water below.

This is useful as:

-the water under the ice can remain liquid allowing the environment to persist.

Why does water have a high latent heat of vaporisation, what does this mean and why is this important for living organisms(2).

The H-bonds have to be broken to allow water to evaporate.

It takes a lot of energy to break the many H-bonds

This is useful as:

-sweating and panting cool animals

-water evaporating off leaves keeps plants from overheating

Why is water a reactant, and why is this important for living organisms(1).

The hydrogen and oxygen are required by some of life's processes.

Such as hydrolysis reactions and photosynthesis.

Why is ice a good insulator, and why is this important for living organisms(1).

Ice doesn't heat very well.

This is useful as:

-it keeps liquid water underneath from freezing

Why is water transparent, and why is this important for living organisms(2).

Visible light can travel through it.

This is useful as:

-aquatic animals can see

-plants can photosynthesise

Why does water have high surface tension, what does this mean and why is this important for living organisms(1).

Molecules of water don't break their hydrogen bonds easily.

This means that the surface of the water can take some force without breaking

This is useful as:

-small animals can walk on water and use it as their habitat.

What makes water incompressible, and why is this important for living organisms(1).

It doesn't change volume when put under pressure.

This is useful as:

-Plant cells become turgid and act as structural support for the plant

What elements make up the 4 main biomolecules?

Carbohydrates-C,H,O

Protein-C,H,O,N,S

Lipids-C,H,O

Nucleic acid-C,H,O,N,P

What are the monomers/building blocks of the 4 main biomolecules?

Carbohydrates-monosaccharides

Protein-amino acids

Lipids-3 fatty acids and 1 glycerol

Nucleic acid-nucleotides

What is the name of the polymer/macromolecule of the 4 main biomolecules?

Carbohydrates-polysaccharide

Protein-polypeptide

Lipids-triglyceride

Nucleic acid-nucleic acid

What is the name of the bonds in the 4 main biomolecules?

Carbohydrates-glycosidic

Protein-peptide

Lipids-ester

Nucleic acid-phosphodiester

What sort of reactions for all 4 biomolecules and what sort of reactions split them?

Condensation reaction forms

Hydrolysis splits

What are the functions of the 4 main biomolecules?

Carbohydrates-energy store, energy supply and structure

Protein-structure, transport, enzymes, antibodies and some hormones

Lipids-membranes, energy supply, thermal insulation.

Nucleic acid-carry the instruction for life.

What are the properties of monosaccharides, disaccharides and polysaccharides?

Mono:

-soluble in water

-sweet

-component of nucleic acids

Di:

-soluble in water

-sweet

poly:

-insoluble in water

-storage

-structural

What is a pentose sugar and give 2 examples.

A sugar with a 5 carbons.

Such as ribose and deoxyribose.

What is a hexose sugar and give 2 examples.

A sugar with 6 carbons

Such as alpha glucose and beta glucose.

What is the difference between alpha and beta glucose?

The hydroxyl group on carbon 1 of alpha glucose is below the ring whereas the hydroxyl group on beta glucose is above the ring.

How is a disaccharide formed?

A condensation reaction between 2 monosaccharides produces a glycosidic bond between them and a water molecule.

What are polysaccharides?

molecules composed of many glucose molecules joined in a chain by glycosidic bonds formed from condensation reactions

What are the 3 storage polysaccharides and how are they suited for this?

Amylose, amylopectin and glycogen.

They are large and insoluble so the water potential of cells aren't affected.

1-6 bonds allow branches so there are many end points for enzymes to bind to, this allows for a fast release of glucose.

Coiled helix structure allows for compact storage.

Alpha glucose joined by 1-4 and 1-6 glycosidic bonds is very stable.

State celluloses function and why it is suited to it.

Structure

Cellulose forms chains rather than coils which so can form crosslinks with other chains to create a strong structure.

It is insoluble to water so retains its physical properties when wet.

Explain how cellulose molecules make up cellulose fibres.

Cellulose molecules can crosslink with H-bonds to other cellulose molecules. This forms a microfibril. These can further combine into microfibrils which then further combine into cellulose fibres

What are the 2 main types of lipids?

triglycerides and sterols (phospholipids are modified triglycerides)

Why are lipids more efficient energy stores than carbohydrates?

Lipids have less oxygen and therefore more hydrogen, this makes them more efficient as the majority of the energy is related to hydrogen atoms.

Why are lipids macromolecules and not polymers?

They are large molecules but aren't made of repeating units.

What is the difference between fats and oils?

Fats are solid at room temperature whereas oils are liquid at room temperature

Describe the structure of a triglyceride, including the molecules that make it, the bond type and what the bonds form between.

Triglycerides are made up of 3 fatty acids joined to a glycerol molecule by ester bonds. these form between a hydroxyl group on the glycerol and the OH part of the carboxyl on a fatty acid.

Explain the difference between saturated and non saturated fats structurally, functionally and how this effects their state at room temperature.

Saturated fats have no C=C double bonds so every carbon atom is bonded to the maximum amount of hydrogen. This means that the carbon chain is straight so can be more compact (solid at room temperature).

Unsaturated fats have one or more C=C double bond so not every carbon is bonded to the maximum amount of hydrogen. This means that the carbon chain has kinks in it so is less compact (liquid at room temperature).

What sort of triglycerides are in animals, fish and plants? (saturated/unsaturated)

Animals = saturated

Fish = unsaturated

Plants = unsaturated

What are 5 uses of triglycerides?

-Energy store

-thermal insulator

-electrical insulator

-waterproof plants

-buoyancy for aquatic animals