Required Practical 2 Flashcards
Describe how temporary mounts of plant tissue are made
thin section
Put on a slide with stain
Add a coverslip
Describe how the scientist could have used the temporary mounts of leaves to determine the mean number of chloroplasts in mesophyll cells of a leaf
Select a large number of cells at random
You’d then count the number of chloroplasts
Divide the number of chloroplasts by number of cells
The student cut thin sections of tissue to view with an optical microscope explain why it was important that these sections were thin
This allows more light through
And a single layer of cells to be seen
When the student was making their coverslip slides roger were told to ensure that they did not move the coverslip sideways. Explain why
This is to prevent the cells from rolling on top of each other
Also to prevent any damage to the cells
Mitosis is important in the life of an organism. Give two reasons why
Growth and increasing cell number
Repair and replace cells
Produces genetically identical cells
Asexual reproduction
Explain why the biologist chose to examine 200 cells
More representative as it’s a large sample
Describe how temporary mounts are made
Thin section
Put on a slide with stain
Add a coverslip
Describe how the scientists could have sued the temporary mounts of leaves to determine the mean number of chloroplasts in mesophyll cells of a leaf
Select a large number of cells at random
Count no.of chloroplasts
Divide the no.of chloroplasts by number of cells
Why would you only use the first 5mm from the tip of an onion root
This is where dividing cells are found
You’ll find soft tissue that will squash
Length that fits under the coverslip
Why would you press down firmly on the coverslip
Thin layer of cells spread out so light can pass through nuclei
What is the name given to the division of cytoplasm during the cell cycle
Cytokinesis
Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for his root tip was accurate
Examine a large number of field of view, to ensure a representative sample
Repeat count to ensure figures are correct
Only count whole cells to standardise counting
A scientist treated growing tips of onion root with a chemical that stops roots growing. After 24hours he prepared a stained squash of these root tips. How does the chemical stop the growth of roots
Chemical used would stop anaphase (cell division)
By preventing the spindle fibres from forming
This would not allow the separation of sister chromatids,
So no new cells are added to root tip
A different set of results was obtained when the count was repeated on another occasion with a different garlic root tip. Give two reasons for the difference in results
Different types of garlic
Different age of root tip
Different water availability
different time of day
Describe how the student makes a temporary mount o;this root tip tissue to observe cells in different stages of the cell cycle using an optical light microscope
Place end section of root tip in HCL
Wash end section of root tip in water
Cut tip from root section and place onto a microscopic slide
Add stain to distinguish the chromosomes
Breaks up tissue with a mounted needle
Cover with coverslip and apply pressure gently
