Topic 1: Cells

Describe the difference between magnification and resolution

Magnification refers to the enlargement of an image, its how big an object looks under the microscope

Resolution is how clear and detailed the image is and is the ability to distinguish between two points. (so a higher resolution gives a sharper image)

Describe the advantages and disadvantages of using a light microscope

Advantages:

• Cheap and easy to use

• Can see living things

Disadvantages:

• Low magnification and resolution

Describe the advantages and disadvantages of using an electron microscope

Advantages:

• Can see tiny details

• Higher magnification and resolution

Disadvantages:

• Expensive

• Can’t look at living things

What are the differences in magnification and resolution between electron and light microscopes

Light Microscope:

Magnification = up to about 1,500 times

Resolution = about 200 nanometers

Electron Microscope:

Magnification = up to about 2,000,000 times

Resolution = Around 0.2 nanometers

Why can Electron microscopes magnify much more + show much finer details than Light microscopes?

They use a beam of electrons instead of light

Microscope diagram

Eye Piece Function

Magnifies the image

Objective Lens

captures and reflects the light reflected from an object

Nose Piece

Holds the objective lenses and attaches them to the microscope head

Stage

Where the slides are placed for observation

Stage Clips

holds the slides in place

Rough Focus Wheel

to move the objective lenses towards or away from the slides

Fine Focus Wheel

to sharpen the focus quality of the image after using the rough focus wheel

Iris Diaphragm

Allows you to adjust the amount of light passing through

Light

Projects light onto the slide to see what is on it

Name a piece of apparatus that you can use to help measure a specimen

eyepeice graticule

Magnification Formula

magnification = size of image/size of real object.

Converting between units

Onion cells viewed under a microscope

Why was iodine solution added to the layer of the onion cells

To stain the cells

Why was a thin layer of onion cells used

To allow light to pass through the cells

Animal Cell

Nucleus

Contains genetic material (DNA)

Cytoplasm

Where chemical reactions happen

Mitrochondria

Respiration releases energy here

Cell Membrane

It controlls what goes in and out

Ribosomes

They make proteins

Plant Cell

Chloroplast

Absorb light for photosynthesis

Vacuole

filled with sap, keeps the cell turgid

Cell wall

made of cellulose, contains its shape

Bacteria Cell

Slime Capsule

Provides protection

Flagella

it allows movement

Plasmid

small circular peice of DNA with the info for things such as ambiotic resistance

genetic material

loop of DNA that has the information to control the bacterium’s activities. (NOT ENCLOSED IN A NUCLEUS)

What are the 3 things only in plant cells

• Vacuole

• Chloroplast

• Cell Wall

Prokaryotes and Eukaryotes

Prokaryotes:

Bacterial cells

• single celled

Eukaryotes:

Animal and Plant

• In you

• Multicellular

Three differences between prokaryotes and eukaryotes

E = has mitrochondria

P = does not

E = has nucleus

P = does not

E = does not

P = has slime capsule

Relative size of bacterial cells (prokaryotic) and animal + plant cells (eukaryotic)

Prokaryotic =

0.2-2.0 micrometers (um)

Eukaryotic =

10-100 micrometers (um)

The difference in how the genetic material is found within eukaryotic and prokaryotic cells

Eukaryotic -

• Their genetic material (DNA) is enclosed inside a nucleus

• The genetic material (DNA) is arranged in linear chromosomes

• They also have other genetic material (DNA) in organelles like mitochondria and chloroplasts

Prokaryotic -

• Their genetic material (DNA) is not in a nucleus, its found in a region called the nucleoid

• The genetic material (DNA) is usually in a single circular chromosome

• They can also have small, extra pieces of genetic material (DNA) called plasmids

Specialised Cells in plants + animals

Plants:

• Root Hair Cell

• Xylem cell

• Pholem cell

Animals:

• Sperm Cell

• Nerve Cell

• Muscle Cell

How a muscle cell is specialised (in Animals)

Structure:

• Long + elastic, to contract and relax

• Many mitochondria, to release energy for movement

Function:

• Contracts to produce movements in organs + the body

How a nerve cell is specialised (in Animals)

Structure:

• They are extremely long cells

• They have many branches at both ends to connect to other nerve cells

• They long axes (main branch) is covered in fat to prevent the electrical impulses affecting the surrounding parts of your body (insulation)

Function:

• To carry nerve impulses around your body

How a sperm cell is specialised (in Animals)

Structure:

• Long tail (flagellum), for swimming to the egg

• Lots of mitrochondria, to produce energy for movement

• Head with enzymes, to break into the egg

Function:

• Reaches + fertilises the egg

How a root hair cell is specialised (in Plants)

Structure:

• Large surface area to absorb lots of water and minerals

• No chloroplasts as found below ground, where there is no sunlight

Function:

• Absorbs minerals and water from the soil

What is transported in phloem and xylem

Phloem:

• Sugars and amino acids

Xylem:

• Water and dissolved minerals

What direction are substances transported in phloem and xylem

Phloem:

• Both directions, up + down

Xylem:

• Upwards, from the root to the rest of the plant

Name + describe the transportation process in phloem and xylem

Phloem:

= Translocation

• High pressure pushes sugars from leaves to other parts of the plant

Xylem:

= Transpiration

• Water + dissolved minerals are pulled up the plant

Describe the structure of the vessel phloem

Living cells connected end to end with holes in the walls called sieve plates. These make the substance go up and down the cell

Describe the structure of the vessel xylem

• Long + hollow - long tubes with hollow centre

• Made with dead cells - leaves space for water to move through

• Thick walls - the walls are made of lignin which helps the plant stay strong + sturdy and supports water flow

• Connected cells - the cells are connected from end to end, with holes in their walls that let water move slowly

Phloem + Xylem Diagram

Differences + Similarities between phloem and xylem

Similarities:

• Thick Walls

Differences:

Phloem - living cells, cytoplasm, sugars, energy needed

Xylem - dead cells, no cytoplasm, water, no energy needed

Explain why animals have specialised cells

• They become specialised for its job, they develop different subcellular structures and turn into different types of cells to carry out specific jobs efficiently

• used for repairing and replacing cells, such as skin or blood cells

Specialised cells in animals and plants

Animals:

• In most animal cells, the ability to differentiate is then lost after they become specialised

• The cells that differentiate in mature animals are mainly used for repairing and replacing cells, such as skin or blood cells

• Most types of animal cells differentiate at an early stage

Plants:

• Lots of plant cells don’t ever lose the ability to differentiate

A scientific drawing of a root hair cell observed using a light microscope.

What is diffusion

Diffusion is the net movement of particles from an area of high concentration to an area of low concentration down a concentration gradient until it is evenly spread out

Where does diffusion happen

In both solutions and gases - because the particles in these substances are free to move about randomly

How to predict which way substances will move across a cell membrane.

Just like with diffusion in air, particles flow through the cell membrane from where there’s a higher concentration (more of them) to where there’s a lower concentration (fewer of them)

There only moving about randomly, so they go both ways - but if there are a lot more particles on one side of the membrane, there’s a net (overall) movement from that side

What substances are transported in and out of cells by diffusion

• Oxygen + Carbon dioxide in gas exchange

• The waste product urea from cells into the blood plasma for excretion in the kidney

What affects diffusion

• Temperature - the higher the temperature, the faster the rate of diffusion. This is because the particles have more energy, so they move around faster

• Surface Area - the larger the surface area (eg, the cell membrane), the faster the rate of diffusion. This is because more particles can pass through at once

• Concentration Gradient - The bigger the concentration gradient, the faster the rate of diffusion. This is because the net movement from one side is greater.

What is osmosis

Osmosis is the movement of water particles from high concentration (of water) to low concentration (of water) across a partially permeable membrane

What is a partially permeable membrane

A partially permeable membrane is just one with very small holes in it. So small only tiny molecules (like water) can pass through them, as bigger molecules (like sucrose, a sugar) can’t

What happens during the movement of water molecules through the membrane during osmosis

The water molecules pass both ways through the membrane during osmosis. This happens because water molecules move about randomly all the time.

Movement of water molecules in and out of cells

If a cell is short of water, the solution inside it will become quite concentrated (there’ll be a low concentration of water molecules). This means the solution outside the cell is more dilute (there’s a higher concentration of water molecules), and so the water will move into the cell by osmosis.

If a cell has lots of water, the solution inside it will be more dilute, and water will be drawn out of the cell and into the fluid outside by osmosis.

what is osmosis a type of

diffusion

Using ideas about osmosis to explain why maintaining constant internal conditions in living organisms is important.

It manages osmosis balance, which allows water to go in and out of the cell through the cell wall without the cell bursting or shriveling. Maintaining isotonic conditions ensures efficient cellular function and survival.

osmosis in animal cells

Animal cells burst if too much water enters the cell as they do not have a cell wall to hold the cell together.

If animal cells loose too much water, they shrivel

Differences between diffusion + osmosis

• Diffusion can involve any type of molecules, such as gases, liquids, or solids, whereas osmosis refers to the movement of water molecules

• Diffusion does not require a membrane as the molecules move freely across the space, whereas osmosis requires a partially permeable membrane

• In diffusion, molecules move in all directions from high concentration to low concentration, whereas in osmosis, water moves from the side with higher water concentration

Write a suitable plan to investigate into the effect of salt or sugar solutions on plant tissue

1. Cut up a potato into identical cylinders and measure their masses

2. Get some beakers with different sugar solutions in them. One should be pure water and another should be a very concentrated sugar solution. then you can have a few others with concentrations in between.

3. Place one potato cylinder in each beaker. Leave them in the beakers for twenty four hours.

4. Take the cylinders out, dry them with a paper towel and measure their masses again.

5. If the cylinders have drawn in water by osmosis, they’ll have increased in mass. If water has been drawn out, they’ll have decreased in mass.

6. Then calculate percentage change in mass and then plot your graph.

Salt and sugar experiment variables

Dependent Variable:

• the cylinder mass

Independent Variable:

• the concentration of the sugar solution

Controlled Variable:

• the volume of solution

• the temperature

• the time

• the type of sugar used

Salt and sugar experiment errors

• If some potato cylinders were not fully dried, the excess water would give a higher mass

• If water evaporated from the beakers, the concentrations of the sugar solutions would change

Use osmosis to explain the effect of placing plant tissue in salt or sugar solutions.

If you put plant tissue in salty or sugary water, water moves out of the cells (because there’s more salt/sugar outside) the cells shrink + the plant becomes floppy.

If you put the plant tissue in pure water, water moves into the cells. The cells swell + the plant stands up straight.

This is because of osmosis - water moves to where there is less water to balance things out.

Calculate percentage change

What is Active Transport

Active Transport is the movement of particles from low concentration to high concentration against the concentration gradient - the way it wants to be going, requiring energy (APT)

What is APT

APT is a molecule produced during respiration that every cell in your body can use for energy

What does active transport do

Active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient). This requires energy from respiration.

Examples of active transport

1. Active transport allows mineral ions to be absorbed into plant root hairs

   from very dilute solutions in the soil. Plants require ions for healthy

   growth

2. It also allows sugar molecules to be absorbed from lower concentrations

   in the gut into the blood which has a higher sugar concentration. Sugar

   molecules are used for cell respiration

Active transport in the gut

Active transport is used in the digestive system when there is a lower concentration of nutrients in the gut, but a higher concentration of nutrients in the blood

here’s how it works:

• when there’s a higher concentration of glucose and amino acids in the gut they diffuse naturally into the blood BUT sometimes there’s a lower concentration of nutrients in the gut than there is in the blood

• This means that the concentration gradient is the wrong way. This is where active transport comes in

• Active transport allows nutrients to be taken into the blood, despite the fact that the concentration gradient is the wrong way. This is essential to stop us starving. It means that glucose can be taken into the bloodstream when its concentration in the blood is already higher than in the gut. The glucose can then be transported to cells, where it’s used for respiration.

Explain why active transport is important for living organisms

It allows substances to move against the concentration gradient, which helps maintain the appropriate balance of substances in the cell.

Some improvements/limitations to a representational model that shows active transport.

Improvements

• show ATP being used

• show different types of transport proteins and how they work

Limitations

• too simple

• not showing movement

Explain the differences between diffusion, osmosis, and active transport.

• Diffusion + Osmosis are passive, whereas Active Transport is active

• Diffusion + Osmosis go from high concentration to low concentration, whereas Active transport goes from low concentration to high concentration

• Diffusion substances are small molecules, Osmosis substances are water molecules, and Active Transport substances are large molecules

Describe how the effectiveness of exchange surfaces is increased

Exchange Surfaces are adapted to maximise effectiveness:

• They have a thin membrane, so substances only have a short distance to diffuse. (Short diffusion pathway)

• They have a large surface area so lots of a substance can diffuse at once

• Exchange surfaces in animals have lots of blood vessels, to get stuff into and out of the blood quickly

• Gas exchange surfaces in animals (eg alveoli) are often ventilated too - air moves in and out

Use ideas about surface area to volume ratio to describe why multicellular organisms need exchange surfaces.

In single-celled organisms, gases and dissolved substances can diffuse directly into or out of the cell across the cell membrane. It’s because they have a large surface area compared to their volume, so enough substances can be exchanged across the membrane to supply the volume of the cell.

Multicellular organisms have a smaller surface area compared to their volume - not enough substances can diffuse from their outside surface to supply their entire volume. This means they need an exchange surface for efficient diffusion.

What does the surface area to volume ratio show

A ratio shows how big one value is compared to another. The larger an organism is, the small its surface area is compared to its volume.

Explain how the small intestine is adapted for exchanging materials

The inside of the small intestine is covered in millions and millions of tiny projections called villi

• Villi increase the surface area so that digested food is absorbed much more quickly into the blood

• Villi have a single layer of surface cells

• Villi have a very good blood supply to assist quick absorption

Explain how gills in fish are adapted for exchanging materials

• Each gill is made of lots of thin plates called gill filaments, which give a large surface area for exchange of gases so the rate of diffusion increases

• The gill filaments are covered in lots of tiny structures called lamellae, which increase the surface area even more

• The lamellae have lots of blood capillaries to speed up diffusion between the water and the blood

• They also have a thin surface layer of cells to minimise the distance that the gases have to diffuse

• Blood flows through the lamellae in one direction and water flows over in the opposite direction,this maintains a large concentration gradient between the water and the blood

• The concentration of oxygen in the water is always higher than in the blood, so as much oxygen as possible diffuses from the water into the blood

Explain how the leaves in plants, are adapted for exchanging materials

• The underneath of the leaf is an exchange surface. It’s covered in little holes called stomata which carbon dioxide diffuses in through and oxygen and water vapour diffuse out of

• The flattened shape of the leaf increases the area of this exchange surface so that it’s more effective

• The walls of the cells inside the leaf form another exchange surface. The air spaces inside the leaf increase the area of this surface so there’s more chance for carbon dioxide to get into the cells

• Has guard cells which can close the stomata to prevent the plant from loosing too much water and wilting