B1 Cell Structure and Transport

Light microscopes

Use beam of light to form image of object. Best they can magnify is x2000. Cheap and can magnify live specimens. Resolving power of 200nm.

Electron Microscopes

Use beam of electrons to form image of object. Magnify up to x2,000,000. Large and expensive. Kept temp, pressure, humidity controlled rooms. Resolving power of 0.2nm.

how do you calculate real size of an object?

image size/ magnification

How do you calculate magnification?

size of image/size of real object

How do you calculate image size?

magnification x real size

What is resolution?

The ability to clearly distinguish the individual parts of an object

What does resolving power do?

affects how much detail can be shown.

Nucleus

Controls the activities of the cell. Contains genes on the chromosomes.

Cytoplasm

A jellylike fluid inside the cell in which the organelles are suspended and where chemical reactions take place needed for life.

Cell membrane

Controls the passage of substances such as glucose and minerals into the cell and controls movements of substances like urea and hormones out of the cell.

mitochondria

structures in cytoplasm where aerobic respiration takes place releasing energy for the cell.

Ribosomes

where protein synthesis occurs

Cell wall

Only in Plant Cells; supports and provides protection

Chloroplast

Contains chlorophyll, a green pigment that absorbs sunlight for photosynthesis and gives plants their green colour.

Vacuole

space in cytoplasm filled with cell sap. Keeps cells rigid to support plant.

Why do root cells not have chloroplasts?

Because they are underground and do not photosynthesise

Eukaryotic cells

all have a cell membrane, cytoplasm and genetic material (DNA) enclosed in nucleus.

Prokaryotic Cells

Example is bacteria - single celled organism. Smaller than eukaryotes. Cytoplasm and cell membrane surrounded by cell wall. Bacterial chromosome is a single DNA loop found free in cytoplasm.

What are plasmids?

small rings of DNA found in some bacteria cells.

What is the slime capsule?

A layer of protective slime around outisde of cell wall found in some bacteria cells.

What are flagella?

long protein strand that lashes about. Used to move around. Found in some types of bacteria.

What are orders of magnitude?

used to make approx. comparisons between numbers or objects

If an object is 10x bigger than another how many orders of magnitude bigger is it?

1

if bigger number divided by smaller number is less than 10...

They are the same order of magnitude.

If bigger number divided by smaller number is around 10 it is...

1 order of magnitude bigger

If bigger number divided by smaller number is around 100 it is...

2 orders of magnitude bigger

When do animal cells differentiate?

in an early stage of development

When a cell differentiates what happens?

it gets different sub-cellular structures that help it peform a particular function.

How are nerve cells specialised?

Carry electrical impulses around the body of an animal. Provide rapid communication system between different parts of the body.

Adaptations of Nerve Cells

- Lots of dendrites to make connections to other nerve cells.
- An axon that carries nerve impulse from one place to another.
- nerve endings/synapses adapted to pass impulses to another cell or between nerve cell and muscle cell using transmitter chemicals.

How are muscle cells specialised?

Able to contract and relax in pairs to move bones of skeletons.

Adaptations of striated muscle cells

- Contain special proteins that slide over each other, making fibres contract.
- Contain many mitochondria to transfer energy needed for the chemical reactions that take place as the cells relax and contract.
- Store glycogen (Chemical that can be broken down and used in cellular respiration) by the mitochondria to transfer energy needed for fibres to contract.

Why are sperm cells specialised?

Need to move a long way and through water/female reproductive system to reach egg and break into it.

How are sperm cells specialised?

- Long tail whips from side to side to help move sperm
- middle section full of mitochondria, which transfer energy needed for the tail to work.
- acrosomes store digestive enzymes for breaking down outer layers of the egg
- acrosomes store digestive enzymes for breaking down outer layers of the egg
- nucleus containing genetic info to be passed on.

What are root hair cells?

Close to tips of growing roots. Help take in water and dissolved minerals. Zylem tissue transports mineral ions throughout the plant and through active transport they are moved into the root hair cell.

Adaptations of root hair cells

- big surface area for water to move into cell
- large vacuole that speeds up movement of water by osmosis from soil across the root hair cell.
- many mitochondria that transfer energy needed for active transport of mineral ions into the root hair

Adaptations of photosynthetic cells

- have chloroplast containing chlorophyll that trap light needed for phototsynthesis
- positioned in continous layers in leaves/ outer layers of stem to absorb as much light as possible
- vacuole that helps keep cells rigid by osmosis. Support stem and and keep leaf spread out.

What is xylem?

the transport tissue in plants that carries water and mineral ions from roots to highest leaves and shoots. Also supports the plant.

How are xylem cells adapted?

- alive when first formed but then lignin builds up in spirals in cell walls. Cells die and form hollow tubes that allow mineral ions and water to move easily through them.
- Spirals of lignin make them strong and help withstand pressure of water moving up the plant.

What is phloem?

specialsed transport tissue that carries food made by photosynthesis around body of plant. Phloem cells form tubes that dissolved food can move through easily where needed.

Adaptations of phloem cells

- Cell walls between cells break down to form sieve plates which allows dissolved food to flow easily to where needed.
- Supported by companion cells. Mitochondria of companion cells transfer energy needed to transport food up and down plant in phloem tubes.

What is diffusion?

net movement of particles from an area of higher concentration to an area of lower concentration.

Why does diffusion occur?

Because of random movement of particles. This movement causes particles to bump into each other, and move them around.

When is the rate of diffusion faster?

when there is a greater difference in concentration. A steeper concentration gradient.

When is the rate of diffusion slower?

When there is only a small difference in concentration.

how do you work out net movement?

Particles moving in - particles moving out

What is the concentration gradient?

The difference between two areas of concentration.

Does diffusion occur up or down the concentration gradient?

down

What happens when there is an increase in temp?

The particles will move faster which means diffusion will occur more rapidly.

Diffusion in cells

dissolved substances move in and out of cells by diffusion across the cell membrane.

What is the cell membrane?

a partially permeable membrane (some substances can diffuse through) E.g oxygen, carbon dioxide, sugars, amino acids, urea.

Where is urea made and excreted?

made in liver and passes through to kidneys where is it excreted.

What is the oxygen journey?

- oxygen needed for respiration passes from air in lungs into red blood cells through cell membrane by diffusion.
- oxygen moves down concentration gradient.
- Increased SA of cell membrane
- Oxygen moves down concentration gradient from red blood cells into respiring muscle cells.

What is the glucose journey?

- glucose taken up by cells in small intestine.

What is a partially permeable membrane?

Membranes that only let some types of particles through.

What does dilute mean?

higher concentration of water, low concentration of solute.

What does concentrated mean

Low concentration of water, high concentration of solute.

What is osmosis?

Special type of diffusion
Movement of water molecules from a dilute solution to a more concentrated solute solution through a partially permeable

How is osmosis different from diffusion?

Osmosis needs a partially permeable membrane and is the movement of water molecules.

What does isotonic mean?

concentration of solutes outside cell = internal concentration

What does hypertonic mean?

Concentration of solutes outside cell is higher than internal concentration

What does hypotonic mean?

Concentration of solutes outside cell is lower than internal concentration

What does the cytoplasm contain?

contains dissolved water and solutes

In the cytoplasm what does the concentration need to be like?

needs to remain relatively constant for reactions to occur and cell to work properly.

What happens if there is a hypertonic solution in an animal cell?

Water is leaving the cell so it could shrivel up

What happens if there is a hypotonic solution in an animal cell?

Water is entering the cell so it could burst.

What happens if there is a isotonic solution in an animal cell?

Water is entering and leaving the cell so it will stay the same.

What is turgor pressure?

water moves into the plant by osmosis causing the vacuole to swell which presses the cytoplasm against the cell wall. Pressure build until no more water can enter cell.

What does turgor pressure do?

makes plant cells hard and rigid whcih keeps plant leaves rigid and firm.

What do plants need the fluid surrounding the cell to be? and why?

always be hypotonic to the cytoplasm. This keeps water moving by osmosis in the right directions and cells turgid.

What happens if the fluid surrounding the cell is hypertonic to the cell contents?

The water will leave by osmosis and the cells won't be firm and swollen but become flaccid as there is no pressure on the cell walls.

What is plasmolysis?

shrinkage of vacuole and cytoplasm due to more loss of water. Cell membrane pulls away from cell wall. Plasmolysed cells die.

How to observe osmosis in plant cells?

Use identical cylinders of potato and put them into different concentrations of sugar solutions and work out the percentage change of each to see how much osmosis affected it.

What is active transport?

Movement of substances from an area of low concentration to an area of high concentration across a partially permeable membrane. This movement is against the concentration gradient.

What substances can be moved by active transport?

Enables cells to move sugars and ions from one place to another through a cell membrane. Cells can absorb ions from dilute solutions.

In order for a lot of active transport to happen what needs to happen?

A cell needs to respire and release a lot of energy.

What do cells doing a lot of active transport need?

a lot of mitochondria and oxygen

examples of active transport

- Plant root hairs absorb minerals such as ions. Nitrate ions are found in very dilute solutions so go against the concentration gradient.
- sugar such as glucose is always actively absorbed out of your gut and kidney tubules into your blood and is done against a large concentration gradient.

What does a large SA: V ratio allow?

sufficient transport of molecules into and out of the cell to meet the needs of the organsim.

When an object gets bigger, what happens to its SA:V ratio

It gets smaller

If the SA:V ratio is large what does that mean?

the diffusion distances are short and that simple diffusion will suffice for the exchange of materials.

Why is it difficult to exchange materials with large and complex living organsims?

- Gases and food molecules no longer reach every cell in organism by simple diffusion.
- metabolic waste can't be removed fast enough to avoid poisoning the cells.

Adaptations for exchanging materials

- large SA exchange can take place over
- thin membrane or being thin to provide a short diffusion path
- In animals, efficient blood supply moves diffusing substances away from exchange surfaces and maintains steep concentration gradient.
- In animals, being ventilated makes gas exchange more efficient.