B1 - cell structure and transport

magnification = ...

size of image/size of real object

What is the difference between electron and light microscopes?

Light microscopes magnify up to about x2000 and have a resolving power of 200nm

electron microscopes magnify up to about x2 million and have a resolving power of around 0.2nm

An animal cell contains...

Nucleus - controls all the cell's activities
cytoplasm - a liquid gel in which most chemical reactions take place
cell membrane - controls substances which move in and out of a cell
mitochondria - where aerobic respiration takes place
ribsomes - where protein synthesis takes place

What features do only plant cells have?

Chloroplasts - used to absorb light for photosynthesis
Vacuole - cell sap made of sugar and salts that keeps the cell rigid
Cell wall - made of cellulose and strengthens the cell to give it support

What are prokaryotes?

mainly bacteria - contain cytoplasm and a cell membrane surrounded by a cell wall. the genetic material forms a single dna loop instead of a nucleus. Some prokaryotes have small rings of dna called plasmids and some bacteria have a flagellum to help with movement.

What are eukaryotes?

mainly animal and plant cells - eukaryotic cells all have a cytoplasm, cell membrane and a nucleus.

What is differentiation?

As an organism develops, cells differentiate to form different types of cell.

What happens when an animal cell becomes a specialised cell?

It gains sub-cellular structures which help it to carry out specific functions

Examples of specialised animal cells are...

- nerve cells
- sperm cells
- muscle cells

Why would an animal cell need to be specialised?

animal cells become specialised to function with a tissue, organ, or an organ system or whole organisms.

Why would a plant cell need to be specialised?

plant cells, similarly, become specialised to function in a tissue, organ, organ systems or organisms

examples of specialised plant cells are?

- root hair cells
- photosynthetic cells
- xylem cells
- phloem cells

What is diffusion?

The spreading out of particles of any substance in a solution or gas resulting in a movement from high to low concentration with the concentration gradient

What can the rate of diffusion be affected by?

- difference in concentrations
- temperature
- available surface area

Examples of substances and gases that move in and out of a cell by diffusion?

glucose and urea
oxygen and carbon dioxide

What is osmosis?

Osmosis is a special case of diffusion where water moves from a high water concentration to a low water concentration over a partially permeable membrane.

What does hypertonic, hypotonic and isotonic mean?

if the concentration of solutes in the solution outside the cell is lower than internal concentration, then the solution is hypotonic to the cell

if the concentration of solutes in the solution outside the cell is higher than internal concentration, then the solution is hypertonic to the cell

if the concentration of solutes in the solution outside the cell is the same as internal concentration, then the solution is isotonic to the cell

What are dangers when osmosis occurs?

If the solution outside the cell is much more dilute than inside the cell, water moves in by osmosis causing the cell to swell and eventually, burst.

If the solution outside the cell is much more concentrated than inside the cell, water moves out by osmosis causing the cell to shrivel up

What is turgor in plants?

plants rely on osmosis to support the stem and leaves. Water moves into the cell by osmosis which causes the vacuole to swell and presses the cytoplasm to the cell wall. The pressure builds up until no more water can enter the cell. This is known as turgor pressure.

What is plasmolysis?

when more water is lost by osmosis in plant cells causing the vacuole and cytoplasm to shrink which eventually leads to the cell membrane to pull away from the cell wall

What is active transport?

Active transport is when the net movement of particles goes from low to high concentration against the concentration gradient but it requires energy.

What is an example of active transport in animals?

Active transport allows sugar molecules used for cell respiration to be absorbed from the low concentrations in the gut to the high concentrations in the blood.

What is an example of active transport in plants?

Active transport allows plant root hairs to absorb minerals ions from the dilute solution in the soil against the concentration gradient

As organisms increase in size, what happens to their surface area to volume ratio and why is this important?

As organisms grow in size, their surface area to volume ratio decreases which makes it harder for organisms to exchange materials quickly.

What do large organisms have to combat their small surface area to volume ratio?

In many large organisms, they have special exchange surfaces which are large in surface area and have thin walls. This creates a short diffusion path.

How to prepare a slide for using a microscope?

Use tweezers to obtain an epidermal tissue

add a drop of water onto a clean slide

place the epidermal tissue onto the glass slide

Add a drop of iodine to stain the the cell so structures within the cell can be observed

add a cover slip onto the slide

avoid smudging the glass slide or trapping air bubbles under it.

How to use a microscope to look at a specimen?

clip the slide onto the stage

use the lowest powered objective lens

use the coarse adjustment knob to bring the stage right below the lens and then use the knob to move the stage gradually downwards until the object is roughly in focus

adjust the fine- adjustment knob until a clear image is obtained

draw an image of the object or repeat with a higher magnification.

Investigating osmosis through potato cylinders?

Use a cork borer to cut 5 cylinders of the same diameter

use a scalpel and ruler to trim each potato cylinder so they’re the same length

measure the mass of each potato and record in a table

measure 10cm volume of sugar and salt solution and pour into each boiling tube. they should vary in concentration of sugar and salt. one should be distilled water

add a potato cylinder to each tube and wait for a specific time

remove the potatoes and record the length and mass