investigating mitosis and cell specialisation

Question 1

• explain how to prepare and stain a root tip in order to observe the stages of mitosis

Answer 1

cut 1 cm from the tip from a growing root. it needs to be the tip because that’s where growth occurs.

prepare a boiling tube containing 1 M hydrochloric acid and put it iun a water bath at 60 degrees celcius

transfer the root tip into the boiling tube and incubate for about 5 minutes

use a pipette to rinse the root tip wll with cold water. Leave the tip to dry on a paper towl

place the root tip on a microscope slide and cut 2 mm from the very tip of it. get rid of the rest

use a mounted needle to break the tip open and spread the cells out thinly

add a few drops of stain and leave it for a few minutes. the stain will make the chromosomes easier to see under a microscope.

place a cover slip over the cells and push down firmly to squash the tissue. this will make the tissue thinner and allow light to pass through it. Dont smear the cover slip sideways

now you can look at all the stages of mitosis under an optical microscope

Question 2

• how can you observe cells using an optical microscope

Answer 2

start by clipping the slide youve prepared onto the stage

select the lowest powered objective lens

use the coarse adjustment knob to bring the stage up yo just below the objective lens

look down the eyepiece . use the coarse adjustment knob to move the stage downwards, away from the objective lens until the image is roughly in focus

adjust the focus with the fine adjustment knob, until you gt a clear image of whats on the slide

if you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus

Question 3

• formula for miotic index

Answer 3

miotic index = NUMBER OF CELLS WITH VISIBLE CHROMOSOMES/ total number of cells observed

Question 4

• explain what the miotic index tells us

Answer 4

lets you work out how quickly the tissue is growing and if there’s anything weird going on. a plant root tip is constantly growing, so you expect a high miotic index.

in other tissue samples, a high miotic index could me that tissue repair is taking place or that there is cancerous growth in the tissue

Question 5

• what can we use to calculate the size of a cell

Answer 5

a micrometer and a graticule

Question 6

• how is an eyepiece graticule used

Answer 6

an eyepiece graticule is fitted onto the eyepiece. its like a transparent ruler with numbers, but no units

Question 7

• how is micrometer used

Answer 7

the stage micrometer is placed on the stage- it is a microscope slide with an accurate scale and its used to work out the value of the divisions on the eyepiece graticule at a particular magnification

this means that when you take the stage micrometer away and replace it with the slide containing your tissue sample, youll be able to measure the size of the cells

Question 8

• how do we use a graticule and micrometer to calculate the size of cells

Answer 8

Line up the eyepiece graticule abd the stage micrometer

each division on the stage micrometer is o.1 mm long

at this magnification 1 division on the stage micrometer is the same as 4.5 divisions on the eyepiece graticule

to work out the size of 1 division on the eyepiece graticule you need to divide 0.1 by 4.5

so if you looj at a cell under the microscope at this magnification and it 4 eyepiece divisions long, you know it measures 0.088

Question 9

• where are artifacts most common

Answer 9

in electron micrographs because specimens need a lot of preparation before you can view them under an electron microscope,

Question 10

• explain how the first scientists avoided artifacts

Answer 10

repeatedly preparing specimens in different ways.

if an object could be seen with one preparation technique, but not another it was more likely to be an artifact than an organelle

Question 11

• define the epithelial tissues

Answer 11

found in animals and consist of sheets of cells

they line the surfaces of organs and often have a protective or secretory function

Question 12

• define the Xylem

Answer 12

occurs in plants and is made up of a number of similar cell types.

it is used to transport water and mineral ions throughout the plant and also fives mechanical support

Question 13

• what tissues is the stomach made up of

Answer 13

muscles to churn and mix the stomach contents

epithelium to protect the stomach wall and produce sectretions

connective tissue to hold together the other tissues

Question 14

• what tissues is a leaf made of

Answer 14

palisade mesophyll made of leaf palisade cells that carry out photosynthesis

spongy mesophyll adapted for gaseoujs diffusion

epidermis to protect the leaf and allow gaseous diffusion

phloem to transport organic materials away from the lear

xylem to transport water and ions into the leaf

Question 15

• what does the digestive system do

Answer 15

the digestive system digests and processes food. it is made up of organs that include the salivary glands, oesophagus, stomach, duodenum, ileum, pancreas and liver

Question 16

• what does the repiratory system do

Answer 16

used for breathing and gas exchange

it is made up of organs that include the trachea, bronchi and lungs

Question 17

• what does the circulatory system do

Answer 17

pumps and circulates blood it is made up of organs that include the heart, arteries and veins