Cells

Describe the fluid mosaic model

• Fluid = phospholipids are constantly moving.

• Mosaic = different proteins embedded throughout.

Name three structures found in some prokaryotic cells, but not found in all prokaryotic cells.

Capsule, plasmid, flagellum.

What are the differences between an optical microscope, TEM and SEM?

Optical microscope

Detects living cells.

Detects colours, stains, dyes.

Low resolution, as it cannot see small organelles.

Relatively straightforward sample preparation.

TEM (Transmission Electron Microscope)

High resolution, can see very small organelles and internal structures.

Can view dead specimens only.

Can only obtain black and white images.

More complex specimen preparation.

SEM (Scanning Electron Microscope)

Higher resolution than optical.

Gives 3D images.

Less complex preparation of specimens.

Thicker specimens can be used.

Can only view dead specimens.

Can only obtain black and white images.

Cannot see internal structures of cell.

Describe the techniques used by optical microscopes, TEM and SEM.

1. Optical microscope

Uses light waves and lenses to magnify an object.

It has a relatively long wavelength and low resolution.

Specimen must be thin enough, one cell thick, to allow light to pass through.

2. TEM (Transmission Electron Microscope)

Beam of electrons is transmitted through the specimen.

Shorter wavelength of light than optical.

Specimen must be very thin and stained using electron-dense substances.

3. SEM (Scanning Electron Microscope)

Electrons are reflected off the surface of the object rather than passing it through.

Produces a 3D image of the external structure of the cell.

What is the function of the mitochondria for aerobic respiration?

The site of aerobic respiration.

Name o types of molecules from which a ribosome is made.

RNA, protein, polypeptide, amino acid, ribosomal RNA.

Why do scientists use a very thin slice of tissue with an optical microscope?

To create a single layer of cell tissues, so light can pass through.

Describe the role of organelles in the production and release of enzymes by animal cells.

1. DNA in the nucleus codes for the enzyme.

2. Ribosomes produce the enzymes.

3. Rough endoplasmic reticulum transports, modifies, processes enzymes.

4. Mitochondria produces ATP.

5. Golgi apparatus modifies, processes, packages, transports enzymes.

6. Vesicles move to cell surface membrane.

7. Vesicles fuse with the cell surface membrane.

How did viruses become able to infect other species of frog?

Mutation in the viral RNA/genetic material.

Altered tertiary structure of the viral attachment protein.

Allows its attachment protein to bind to receptors of other species.

Give three ways a student could ensure they produce a correct biological drawing of a tissue or of a cell.

Use single continuous joined lines;

do not use sketching

do not use shading

add magnification scale

Name three structural features that are found in all virus particles.

Genetic material codes for viral protein.

Capsid protects the genetic material RNA and DNA.

Attachment proteins bind to receptors on cells.

Explain why viruses are described as acellular and non-living.

Acellular because they have no cell surface membrane

They’re non-living as they have no metabolic reactions.

Give one reason why antibiotics are not effective against viruses.

Do not have bacterial structural enzymes

do not have metabolic processes,

do not have a murein cell wall.

Describe two functions of the Golgi apparatus in eukaryotic cells.

modifies, packages, transports lipids; and forms vesicles.

Describe one difference between the structure of DNA in a prokaryotic cell and in a eukaryotic cell.

Circular not linear,

not associated with histone proteins

No introns.

Outline similarities and differences between the structure of chloroplasts and mitochondria.

Similarities

double membrane

both contain circular DNA

both contain ribosomes.

Differences

Grana vs cristae

Stroma vs matrix

pigments vs no pigments

starch grains vs no starch grains.

Describe the structure and function of the nucleus.

Nuclear pores are found through the nuclear envelope.

Nuclear envelope is a double membrane that surrounds the nucleus.

Chromatin is the DNA and associates with histone proteins.

Nucleolus

Stores genetic information that codes for polypeptides

DNA replication occurs

production of mRNA and tRNA

production of rRNA ribosomes.

Name the main polymer that forms the plant cell wall and fungal cell wall.

Plant cell wall, cellulose; fungal cell wall, chitin.

Name two features of all prokaryotic cells that are not features of eukaryotic cells.

DNA freely in the cytoplasm;

DNA not associated with histone proteins;

Muerin cell wall;

circular DNA;

no membrane-bound organelles.

Suggest and explain how viruses become able to infect other frog species, when they previously only infected one species of frog.

Mutations in the viral DNA altered tertiary structure of the viral attachment protein, allows attachment proteins to bind to receptors of other species.

Why might organelles not be visible in a TEM image?

Organelles are not stained.

State one advantage of using a TEM rather than an SEM.

A higher resolution and you can view the internal structures.

Give differences between DNA in chloroplasts and DNA in the nucleus.

DNA in chloroplast is shorter

fewer genes

DNA is circular, not linear

not associated with histone proteins

introns are absent but present in nuclear DNA.

Give differences between an optical microscope and a TEM.

Optical has longer wavelengths of light. Transmission has shorter wavelengths.

Optical, lower resolution,

transmission electron, higher resolution.

Name an organelle or structure found in both chloroplasts and prokaryotic cells.

ribosomes

Describe how prokaryotic DNA is arranged compared with human DNA.

Prokaryotic DNA is circular,

not associated with histone proteins,

it's present as plasmids.

Why do white blood cells stain differently from red blood cells?

White cells have a nucleus that stains, red blood cells do not have a nucleus.

Name molecules or substances associated with ribosomes.

RNA, nucleotides, proteins, polypeptides, amino acids.

State how to improve a scientific drawing.

Don't use shading

add labels

don't cross label lines

add magnification scale.

Compare how a TEM and an optical microscope work, including their limitations.

How they work - Transmission electron microscope uses electrons and optical uses light.

TEM focuses using magnets and optical uses glass lenses.

2. Resolution - TEM allows greater resolution.

So with TEM smaller organelles and cell structures can be observed.

3. Specimens - TEM view only dead, and optical view live specimens.

TEM requires thinner specimens.

4. Images - TEM does not show colour, optical can.

5. Preparation - TEM requires a more complex, time-consuming preparation.

What happens when a cell or organelle is placed in a solution with the same water

Osmosis does not occur.

organelle does not shrink or burst.

What is the function of a mitochondrion?

The site of aerobic respiration.

Why is a TEM used to examine cell organelles?

It can produce high-resolution images

can see internal structures of organelles.

Describe how chloroplasts can be isolated by cell fractionation.

Break open cells and remove debris

solution is cold, isotonic and buffered.

Solution spun at a high speed

Second pellet is chloroplasts.

What is the purpose of cristae in mitochondria?

Increasing the capacity for ATP synthesis by increasing the surface area of the inner membrane where oxidative phosphorylation occurs.

State two roles of the rough endoplasmic reticulum (RER).

It contains ribosomes where protein synthesis occurs.

It transports, modifies and processes the proteins once they have been synthesized.

Give evidence that mitochondria evolved from prokaryotes.

They have circular DNA

they have 70S ribosomes

their DNA has no introns

their DNA isn't associated with histones.

What happens to Golgi vesicles after packaging their contents?

They move the contents to the cell membrane and then fuse with it, releasing the content to the outside of the cell

What is the function of a chloroplast?

It is the site of photosynthesis where light energy is used to produce carbohydrates.

Describe adaptations of plant cells for photosynthesis.

.

They contain chlorophyll in chloroplasts to absorb light energy. The large permanent vacuole pushes the chloroplast to the edge of the cell. They have a thin permeable wall to absorb carbon dioxide

Describe two features of red blood cells and explain their usefulness.

They have no nucleus or organelles to maximise the volume of haemoglobin.

They have a biconcave shape that allows them to bend and flow smoothly through the capillaries.

Name features common to both prokaryotic and eukaryotic cells.

Cell membrane

ribosome

cytoplasm

DNA.

Which structures can and cannot be seen using a light microscope?

It can see the nucleus and mitochondria.

It cannot see ribosomes, nucleolus, lysosomes.

Why do electron microscopes have a higher resolution than light microscopes?

Electrons have a shorter wavelength than light.

Why is an electron microscope used to identify cell organelles?

A higher resolution is needed to see the internal structure of organelles.

Why can organelles not be identified in a red blood cell using an electron microscope

The cytoplasm of a red blood cell is filled with haemoglobin.

It does not contain any organelles.

Describe how a TEM produces an image.

Electrons pass through the specimen.

The denser parts absorb more electrons.

The denser parts therefore appear darker.

Electrons have a shorter wavelength, so produce a high resolution.

State limitations of a TEM compared with an optical microscope or SEM.

Specimens cannot be living as it is viewed in a vacuum.

Specimens must be very thin.

Artifacts can be present.

The staining method is complex and the preparation time is therefore long.

Only 2D images can be produced versus 3D images with SEM.

Only black and white images can be produced versus colour images with an optical microscope.

State advantages of an SEM compared with a TEM.

Specimens do not need to be as thin.

An SEM produces 3D imaging.

TEM produces 2D images.

Describe how to use an eyepiece graticule to measure a specimen.

Measure a specimen using an eyepiece graticule.

Calibrate the eyepiece graticule against a stage micrometer.

Take multiple measurements and calculate a mean.

Describe how to prepare a temporary mount of plant tissue.

Add a drop of water to the slide.

Get a section of the plant tissue and place on the slide, floating it on the water.

Stain with iodine in potassium iodide.

Lower cover slip at an angle using a mounted needle to avoid trapping air bubbles.

Compare the cell walls of plants, bacteria and fungi.

Plant cell cellulose cell wall

bacteria murein cell wall

fungi chitin cell wall.

What are ribosomes made of and where are they found?

Ribosomes are made of RNA and protein, found in the cytoplasm attached to the rough endoplasmic reticulum.

Describe 80S ribosomes.

80S type found in the eukaryotic cells

rough endoplasmic reticulum, ribosomes present on the outside and they synthesise proteins, produce proteins.

Describe the smooth endoplasmic reticulum.

Synthesise lipids

What do lysosomes store?

hydrologic enzymes called lysozymes

State the functions of the cell wall.

has high tensile strength and prevents osmotic lysis in plant cells.

What is the purpose of using a mounting needle when preparing a slide?

Is to avoid any air bubbles.

Give the equation used to calculate actual size.

I = AM

What is meant by actual size?

Actual size is the true size of the object in real life.

What is meant by image size?

The image size, the size of the diagram or drawin

What is homogenisation during cell fractionation?

Homogenise the cells by blending them in a solution or break open the cells by blending them in a solution.

Why can thicker bacterial capsules contribute to lung disease?

Thicker capsules are less likely to bind to murein cell wall, reduce phagocytosis, for more bacterial division.

Name molecules coded for by genes or produced from gene expression.

RNA, pre-mRNA, polypeptide, protein and RNA.

Why are antibiotics ineffective against viruses?

They do not have metabolic processes

do not have a cell wall

do not have ribosomes.

Name three features of HIV particles that are not found in bacteria..

Capsid, reverse transcriptase, attachment proteins

Why do unsaturated fatty acids cause the cell membrane to be more fluid?

The double bonds cause kinks in the fatty acid tail, causing the phospholipids to be further apart.

What are the main 2 effects of an extremely high temperature on cells and why

Enzyme activity decreases as the active sites denature.

Membrane fluidity increases due to the denaturing of carrier and channel proteins and the phospholipids gaining more kinetic energy.

suggest one advantage of the different percentage of cholesterol in red blood cells

Red blood cells are freely in the blood.

They're not supported by other cells

so cholesterol helps to maintain their shape

Describe the effect of a hypotonic solution on an animal cell.

A solution with a higher water potential and lower solute concentration than inside the cell.

Water enters the cell by osmosis, down a water potential gradient, causing the cell to swell and eventually burst. This is called osmotic lysis.

Describe the effect of a hypertonic solution on an animal cell.

A solution with a lower water potential and higher solute concentration than inside the cell.

The concentrated solution has a lower water potential than the cell, so water leaves the cell by osmosis, causing the cell to shrink.

Describe the effect of an isotonic solution on an animal cell.

Water potential same inside cell and in solute

There is no net osmotic movement of water because there is no water potential gradient. The size of the cell will remain the same.

Describe the effect of a hypertonic solution on a plant cell.

A solution with a lower water potential and higher solute concentration than inside the cell.

The concentrated solution has a lower water potential than the cell, so water leaves the cell cytoplasm by osmosis, causing the vacuole to shrink. The cytoplasm shrinks, leaving gaps between the cell membrane and the cell wall. This is called plasmolysis.

Describe the effect of a hypotonic solution on a plant cell.

A solution with a high water potential and lower solute concentration than inside the cell.

A dilute solution of pure water will have a higher water potential than inside the cell, so water enters the cell by osmosis. The cytoplasm and vacuole gain some water, but because of the high tensile strength of the cellulose cell wall, the cell will not burst. Instead, it will become turgid.

Describe the effect of an isotonic solution on a plant cell.

Water potential same inside cell and in solute

No net osmotic movement.

State the equation for producing a diluted solution from a stock solution and define each symbol.

C1V1=C2V2

Describe the mechanism of active transport.

Movement of molecules from a region of lower concentration to a region of higher concentration, against a concentration gradient, using ATP and carrier proteins.

There are carrier proteins spanning the plasma membrane.

The molecules bind to a complementary binding site on the carrier protein.

ATP is hydrolysed into ADP and inorganic phosphate.

Energy released from the hydrolysis of ATP causes the protein to change shape, and the molecule is released onto the other side of the cell.

How does the number of carrier proteins affect the rate of active transport?

A lower number of carrier proteins means that they become saturated and the rate of active transport will plateau.

Microvilli increase the surface area of the cell membrane, so there is more space for carrier proteins.

Describe intrinsic proteins, carrier proteins and channel proteins.

Intrinsic proteins span the whole membrane and are used for transport.

Carrier proteins are used for large molecules, such as glucose.

Channel proteins are used for charged molecules, such as ions.

Describe extrinsic proteins and their functions.

Extrinsic proteins are on the inner and outer surface of the membrane and do not go all the way through the membrane.

They provide structural support, bind cells together, form recognition sites, act as receptors on the cell-surface membrane for chemicals such as hormones to bind to, allow cells to detect chemicals from other cells, and act as membrane-bound enzymes.

What are glycoproteins and what are their functions?

Glycoproteins are carbohydrate chains attached to proteins in the membrane.

These glycoproteins act as receptors for hormones, neurotransmitters or antigens.

What are glycolipids and what are their functions?

A glycolipid is a carbohydrate bonded to a phospholipid in the membrane.

These act as recognition sites.

They also form hydrogen bonds with the water surrounding the membrane, which helps to maintain the stability of the membrane and helps cells attach to one another, forming tissues.

Describe the location and functions of cholesterol in the cell-surface membrane.

Cholesterol molecules are a type of lipid that sits between the hydrophobic tails in the phospholipid bilayer.

Cholesterol stabilises the membrane by restricting the movement of Phospholipids tail

The movement of substances across cell membranes is affected by membrane structure. Describe how?

Phospholipid bilayer allows movement of non-polar or lipid-soluble substances

Phospholipid bilayer prevents movement of polar or charged or lipid-insoluble substances

Membrane proteins allow polar or charged substances to cross the bilayer

Carrier proteins allow active transport

Channel and carrier proteins allow facilitated diffusion or co-transport

Shape of channel and carrier determines which substances move

Number of channels and carriers determines how much movement;

Membrane surface area determines how much movement

Cholesterol affects Fluidity rigidity and permeability

Describe how temperature affects membrane permeability.

Below 0°C:

There is little kinetic energy. Phospholipids are packed closely together and cannot move very much. Channel and carrier proteins deform, which increases permeability.

Between 0 and 45°C:

The phospholipids can move around and the membrane is partially permeable.

Above 45°C:

The phospholipid bilayer starts to break down and become more permeable. The membrane proteins denature. This increases permeability.

Describe simple diffusion.

Simple diffusion is the net movement of particles (small, uncharged, lipid-soluble molecules) down a concentration gradient, straight across the phospholipid bilayer.

It is a passive process and does not require ATP.

Diffusion limiting factors.

Surface area

Greater surface area of the membrane = more space for particles to move across.

Faster rate of diffusion.

2. Diffusion pathway

Thinner exchange surface = shorter diffusion pathway.

Faster rate of diffusion.

3. Concentration gradient

- Steeper concentration gradient = faster rate of diffusion.

4. Temperature

Higher temperature = particles have more kinetic energy.

Faster rate of diffusion.

5. Type of molecule

- Non-polar molecules generally diffuse faster than polar molecules.

How can the rate of diffusion be increased?

Maximise the surface area.

Maximise the concentration difference, creating a steeper concentration gradient.

Minimise the thickness of the exchange surface, creating a shorter diffusion pathway.

Describe facilitated diffusion and explain what limits its rate.

Facilitated diffusion is the movement (larger molecules or charged particles and ions) down a concentration gradient via channel or carrier proteins.

It is a passive process.

No ATP required

The limited number of channel and carrier proteins in membranes can limit the rate of facilitated diffusion.

Transport proteins can become saturated, so having more carrier and channel proteins allows a greater rate of transport.

Define osmosis.

The net movement of water molecules only down a water potential gradient across a partially permeable membrane.

Describe endocytosis and give an example.

Endocytosis is the process by which cells ingest material from outside the cell by enclosing it with a portion of the cell-surface membrane.

The material is enclosed in vesicles. Endocytosis is used to take in large molecules or materials, such as pathogens during phagocytosis.

Describe exocytosis and give an example.

Exocytosis is when cells release vesicles containing stored materials from inside the cell by fusing the membrane of the vesicle with the cell membranes

This opens the vesicle and releases the contents.

It is used to transport bulk amounts of molecules. An example is the release of neurotransmitters at synapses.

Define Cotransport

Active transport that moves two molecules at once through a co-transport protein.

Describe co-transport in which ATP is used directly.

Co-transport is when a protein binds and moves two molecules at the same time against their concentration gradients.

These molecules have a complementary shape to the tertiary structure of the carrier protein.

The carrier protein also binds and hydrolyses an ATP molecule and uses this energy to open the carrier and move both molecules at the same time. ATP is directly used.

Describe co-transport in which ATP is not used directly.

The co-transport protein also binds and moves two molecules at the same time, but one of these molecules moves by facilitated diffusion.

The concentration gradient of one molecule is used to open the carrier and move the other molecule against its own concentration gradient.

ATP is indirectly used to fuel active transport elsewhere in order to maintain the concentration gradient of the original molecule, so it can keep moving by facilitated diffusion.

Describe the structure of a phospholipid.

Forms a bilayer. Hydrophobic tail points inwards, repelling water molecules. Hydrophilic head points outwards, attracted to water molecules.

What does ATP hydrolysis do in active transport?

ATP hydrolysis releases energy for active transport of X.

What can co-transport do?

Co-transport can move X in and Y out.

How do respiratory inhibitors affect active transport?

less ATP is available

so less active transport or co-transport occurs.

How does increased gene expression affect membrane transport?

Increased gene expression increases transcription, so more carrier proteins are made. This can increase active transport or facilitated diffusion, depending on the question.