B1 - Cell biology

Question 1

Define Eukaryotic Cell

Answer 1

Contain their genetic material enclosed in a nucleus

Question 2

Define Prokaryotic cell

Answer 2

Genetic material not enclosed in a nucleus:
It is a single DNA loop & there may be small rings of DNA called plasmids

Question 3

Prokaryotic cells are (…) in comparison to eukaryotic cells

Answer 3

Much smaller

Question 4

Give the prefixes in standard form:
1) Centi
2) Milli
3) Micro
4) Nano

Answer 4

1) 1 x 10^-2 m
2) 1 x 10^-3 m
3) 1 x 10^-6 m
4) 1 x 10^-9 m

Question 5

Order of Magnitude

Answer 5

Every order of magnitude is 10x greater than before.

10x = 1 order of magnitude
100x = 2 orders of magnitude
1000x = 3 orders of magnitude

Question 6

Function of the Nucleus

Answer 6

To enclose the genetic material

Question 7

Function of the Cytoplasm

Answer 7

Watery solution where chemical reactions take place

Question 8

Function of the Cell Membrane

Answer 8

Controls the molecules that can enter and leave the cell

Question 9

Function of the Mitochondria

Answer 9

Mitochondria are where aerobic respiration takes place

Question 10

Function of the Ribosomes

Answer 10

Sites of protein synthesis

Question 11

Function of the Chloroplasts

Answer 11

Contain chlorophyll & are the sites of photosynthesis

Question 12

Function of the Cell wall

Answer 12

Made from cellulose.
Strengthens the cell.

Question 13

Function of the Vacuole

Answer 13

Filled with a fluid called cell sap.
Helps give the plant cell its shape.

Question 14

How are Sperm cells specialised to carry out their functions?

Answer 14

Genetic information contained in the nucleus - located in the head of the sperm cell.

Long tail + Streamlined - Allows them to swim to the ovum

Midpiece packed full of mitochondria - provide energy for swimming

Enzymes in the head of sperm cell - digest through outer layer of the ovum

Question 15

How are Nerve cells specialised to carry out their functions?

Answer 15

Axon - Carries electrical impulses from one part of the body to another

Myelin - insulates the axon and speeds up transmission of nerve impulses

Synapses - Junctions which allow impulse to pass from one nerve cell to another

Dendrites - Increase surface area so other nerve cells connect more easily

Question 16

How are Muscle cells specialised to carry out their functions?

Answer 16

Muscle cells can contract - Contain protein fibres which can change their length

Packed full of mitochondria to provide energy for muscle contraction

Work together to form muscle tissue

Question 17

How are root hair cells specialised to carry out their functions?

Answer 17

Increases surface area of the root.

Do not contain chloroplasts as they are underground.

Question 18

How are xylem cells specialised to carry out their functions?

Answer 18

Thick walls containing lignin - provides support to the plant.

End walls between cells broken down to form a long tube so water & dissolved minerals can flow easily.

No internal structures - easier for water & minerals to flow.

Question 19

How are Phloem cells specialised to carry out their functions?

Answer 19

Phloem vessel cell & sieve plates allow dissolved sugars to move through the cell interior.

Companion cell - mitochondria provides energy to the phloem vessel cell.

Question 20

Describe the advantages of an electron microscope over a light microscope

Answer 20

• Much greater magnification & resolution than light microscopes

• Enabled biologists to see & understand many more sub-cellular structures

Question 21

What is the equation for number of bacteria after a certain time?

Answer 21

Number of bacteria = 2*(n)

(n) = number of rounds of division

Question 22

Why must Petri dishes & culture media be sterilised before use?

Answer 22

To kill any unwanted microorganisms & it prevents contamination

Question 23

Explain why the lid of the Petri dish should be secured with adhesive tape & stored upside down

Answer 23

To stop the lid from falling off & any unwanted microorganisms entering.

Placed upside down - stops moisture from dripping down onto the bacteria & disrupting the colonies.

Question 24

Explain why in school laboratories, cultures should be incubated at a maximum temperature of 25 C

Answer 24

Reduces the chances that harmful bacteria will grow

Question 25

What is meant by “Zone of inhibition”

Answer 25

A region where the bacteria have not grown

Question 26

Describe the stages of the cell cycle involving mitosis

Answer 26

• DNA replicates to form 2 copies of each chromosome The cell also grows & copies its internal structures. • Mitosis - 1 set of chromosomes pulled to each end of the cell. Nucleus also divides. • The cytoplasm & cell membrane divide to form 2 identical cells.

Question 27

Describe the importance of mitosis

Answer 27

• Essential for growth & development of multicellular organisms • Mitosis takes place when an organism repairs itself • Mitosis happens during asexual reproduction

Question 28

What is meant by a stem cell?

Answer 28

An undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, from which certain other cells can arise from differentiation.

Question 29

Function of stem cells in embryos:

Answer 29

Can be cloned & made to differentiate into most different types of human cells.

Question 30

Function of stem cells in adult animals:

Answer 30

Stem cells from adult bone marrow can form many types of cells including blood cells.

Question 31

Function of stem cellls in plants:

Answer 31

Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant.

Question 32

Describe how stem cells can be used for medical treatment

Answer 32

Therapeutic cloning - embryo is produced with the same genes as the patient. Stem cells from the embryo are not rejected by the patient’s body so they may be used for medical treatment.

Question 33

Risks of the use of stem cells for medical treatment

Answer 33

• Transfer of viral infection • Ethical & religious objections

Question 34

Describe how stem cells can be used for plant cloning

Answer 34

Stem cells from meristems in plants can be used to produce clones of plants quickly & economically. • Rare species can be cloned to protect from extinction • Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.

Question 35

What is meant by diffusion?

Answer 35

The spreading out of particles resulting in a net movement from an area of higher concentration to an area of lower concentration.

Question 36

Describe the factors which affect the rate of diffusion

Answer 36

• Difference in concentrations (concentration gradient) • Temperature • Surface area of the membrane

Question 37

Explain the need for exchange surfaces & a transport system in multicellular organisms

Answer 37

• Their surface area is not large enough for their volume • Cells on the surface get enough oxygen by diffusion however not enough oxygen can diffuse into the cells in the centre of the organism. They are too far away from the surface.

Question 38

Describe how gills increase the rate of transport of gases into & out of the fish

Answer 38

• Oxygen-rich water passes into mouth, then flows over gills where oxygen is transported into bloodstream. • Gills covered in a very large number of fine filaments where gases pass in & out of the blood. • Deoxygenated blood passes into filament. Oxygen diffuses from water into blood. Oxygenated blood returns to body.

Question 39

Adaptations of the filaments to increase rate of diffusion

Answer 39

• Massive surface area. • Thin membrane - short diffusion pathway. • Efficient blood supply - concentration gradient always high.

Question 40

How is the effectiveness of an exchange surfaces increased

Answer 40

• large surface area • thin membrane for short diffusion path • (in animals): efficient blood supply • (in animals, for gaseous exchange): being ventilated

Question 41

What is meant by osmosis

Answer 41

The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

Question 42

Describe the effects of osmosis on animal cells

Answer 42

• If cell placed in water, osmosis takes place - water moves by osmosis from outside cell to inside cell. The cell will expand or could burst. • If cell in concentrated solution, water moves out of cell by osmosis & the cell will shrink.

Question 43

Describe the effects of osmosis on plant cells

Answer 43

• Place plant cell in water - water moves into cell by osmosis & cell will expand. Cell wall prevents cell from bursting so cell become swollen (turgid) • Place cell in concentrated solution - water moves out of plant cell by osmosis. Causes cell to shrink (becomes flaccid)

Question 44

Equation for % change

Answer 44

% change = change in value ________________ X 100 Original value

Question 45

What is active transport?

Answer 45

Moves substances from a more dilute solution to a more concentrated solution (against the concentration gradient). This requires energy from respiration.