Cell Biology

Question 1

What is the difference between light microscopes and electron microscopes?

Answer 1

-Light -> use light and lenses. Let us see individual cells and large subcellular structures
-Electron -> use electrons. Have a higher magnification and resolution and let us see much smaller things in more detail

Question 2

What is the formula for finding the magnification of an image?

Answer 2

Magnification = Image size / Real size

Question 3

How do you prepare a microscope slide?

Answer 3

-add a drop of water
-Place onion epidermal tissue in the water on the slide using tweezers
-Add a drop of iodine solution
-place cover strip on top try not to get any air bubbles

Question 4

How do you look at a slide using a light microscope?

Answer 4

-Clip the slide into the stage
-use lowest powered objective lens to start
-move stage up using coarse adjustment knob
-use same knob to put it roughly into focus
-use fine adjustment knob to put it into focus

Question 5

What is cell differentiation and when does it take place?

Answer 5

-The process of cells developing to become specialised for their specific job
-Happens mainly in the early stages for animal cells
-Happens at any stage for plant cells

Question 6

How are sperm cells specialised?

Answer 6

-long tail
-streamlined head
-lots of mitochondria for energy
-enzymes to digest through egg cell membrane

Question 7

How are nerve cells specialised?

Answer 7

-long to cover distance
-branched connections at their ends to form a network

Question 8

How are muscle cells specialised?

Answer 8

-long so they have space to contract
-lots of mitochondria for energy

Question 9

How are root hair cells specialised?

Answer 9

big surface area for absorbing water and mineral ions from the soil

Question 10

What are chromosomes?

Answer 10

Coiled up lengths of DNA molecules found in the nucleus of cells, containing a large number of genes

Question 11

How many pairs of chromosomes are in a human cell?

Answer 11

23 pairs

Question 12

What is mitosis?

Answer 12

The stage of the cell cycle where it divides. It’s used to grow or replace damaged cells.

Question 13

What happens in the growth and DNA replication stage of the cell-cycle?

Answer 13

-the cell grows and increases its number if subcellular structures
-it duplicates its DNA
-The copied DNA forms X-shaped chromosomes where each arm is an exact duplicate of the other

Question 14

What happens in the mitosis stage of the cell-cycle?

Answer 14

-chromosomes line up in the middle of the cell and cell fibres pull them apart, each arm goes to the opposite side
-Membranes form around each set
-the cytoplasm and cell membrane divide
-divides into 2 daughter cells

Question 15

What is the name of the process where prokaryotic cells replicate?

Answer 15

Binary fission

Question 16

How does binary fission work?

Answer 16

-plasmids replicate
-cell expands and circular DNA strands go to opposite sides of the cell
-cytoplasm starts dividing
-new cell wall starts to form
-divides into 2 daughter cells

Question 17

What is mean division time?

Answer 17

The average amount of time it takes for one bacterial cell to divide into two

Question 18

How are bacteria grown in a lab?

Answer 18

In a culture medium (nutrient broth solution or agar jelly) with all the nutrients they need to grow

Question 19

How do you make an agar plate?

Answer 19

-hot agar jelly is poured into petri dishes
-when it sets wire loops or pipettes are used to put microorganisms in
-bacteria will form visible colonies

Question 20

How can you investigate the effect of antibiotics on bacterial growth?

Answer 20

-evenly cover agar plate with bacteria
-soak paper disks in different antibiotics and put them on top
-antibiotic resistant bacteria will continue growing
-non resistant strains will die and create a clear patch (inhibition zone)
-larger inhibition zone = more effective antibiotic
-use paper soaked in sterile water as a control

Question 21

How do you find the size of an inhibition zone?

Answer 21

By measuring its diameter and use this to find the area

Question 22

What are stem cells and where are they found?

Answer 22

-undifferentiated cells with the potential to turn into any type of cell
-found in early human embryos
-some places in adults (e.g. bone marrow) but they can only turn into certain types of cells (e.g. blood cells)

Question 23

How can stem cells be used to cure disease?

Answer 23

They can be transferred from a healthy adult or an embryo to replace faulty cells in an ill person (e.g. insulin producing cells for a diabetic)

Question 24

How does therapeutic cloning work?

Answer 24

An embryo is made with the same genetic information as the patient so it wouldn’t be rejected by the body.

Question 25

What is the ethical debate around stem cells?

Answer 25

Whether the embryo which is a potential human life should be valued more than curing the existing patients who are suffering

Question 26

How are the stem cells found in the meristems of plants used?

Answer 26

-producing clones -grow more plants of a rare species -grow crops of identical plants

Question 27

What is diffusion?

Answer 27

The gradual movement from areas of high concentration to areas of low concentration. It happens in both solutions and gases

Question 28

How does diffusion take place with cells?

Answer 28

Very small particles like oxygen flow through the cell membrane moving randomly both in and out. The larger the surface area of the membrane, the faster diffusion will happen

Question 29

What is Osmosis?

Answer 29

The movement of water molecules across a partially permeable membrane from an area of high concentration to areas of low concentration.

Question 30

How can you find out how sugar affects plant tissue?

Answer 30

-cut up potato into identical cylinders -measure their initial mass -put into beakers containing sugar solutions with different concentrations and leave for a while -Take them out, dry them and measure their mass again -If they gained water the mass will increase and if the lost water it will decrease

Question 31

How do root hair cells take in minerals using active transport?

Answer 31

-they absorb minerals from a dilute solution using a concentration gradient -this requires energy from respiration

Question 32

How does the human body use active transport?

Answer 32

-when there's more nutrients in the gut than in the blood they diffuse naturally into the blood stream -sometimes its the other way around so active transport is used instead

Question 33

What is an example of cells using diffusion to exchange substances with their environments?

Answer 33

Oxygen and Carbon dioxide are transferred between cells during gas exchange

Question 34

Why is it easy for substances to diffuse in and out of single-celled organisms?

Answer 34

Because they have a larger surface area to volume ratio so enough substances can be exchanged across the membrane to supply the volume of the cell

Question 35

Multicellular organisms need exchange surfaces for efficient diffusion. How are these adapted to maximise effectiveness?

Answer 35

-thin membrane -> short distance to diffuse -large surface area -> more can diffuse at once -lots of blood vessels -> to get things in and out quicker

Question 36

How are the alveoli specialised to maximise the diffusion of O2 and CO2?

Answer 36

-enormous surface area -moist lining for dissolving gasses -very thin walls -good blood supply

Question 37

How are villi specialised to increase the surface area of the small intestine to speed up food absorption?

Answer 37

-single layer of surface cells -very good blood supply

Question 38

How are leaves specialised for the exchange of substances?

Answer 38

-flat shape means large surface area -walls of the cells act as exchange surface -water evaporated from the cells and then escapes by diffusion

Question 39

How do gills act as a gas exchange surface for fish?

Answer 39

-water enters through the mouth and passes the gills -oxygen diffuses into blood and carbon dioxide diffuses into the water -each one is made of gill filaments which increase the surface area -lots of blood capillaries and thin layer of cells