cell biology

Question 1

1) what do microscopes do?

2) what is the equation for magnification?

Answer 1

1) magnify the image of a specimen so that it can appear larger
this makes it easier to observe and study

2) magnification=
image size/real size of the object

Question 2

what are the names and functions of the lenses in a light microscope?

Answer 2

1) the eyepiece lens is the part that you look through

2) the objective lens focuses the image and makes it clearer

Question 3

name pieces of laboratory equipment you could uses to prepare cells to view using a microscope.

Answer 3

(microscope) slide
cover slip
dye / stain
(mounted) needle
pipette / dropper
scalpel
forceps / tweezers

Question 4

what’s the difference between an electron microscope and a light microscope?

Answer 4

electron microscope-
has much higher magnification and resolution/revolving power than a light microscope as it uses electrons.
this means that it can be used to study cells in much finer detail, including sub-cellular structures.

light microscopes-
use light and lenses to magnify, letting us see cells and large subcellular structures like nuclei.

Question 5

what are the divisions of a metre for millimetres, micrometres and nanometres in standard form?

Answer 5

millimetre = 1x10^-3m
micrometre = 1x10^-6m
nanometre = 1x10^-9m

Question 6

to move the objective lens up and down, what dial would you turn?

Answer 6

the coarse/rough focus dial

Question 7

1) what are two ways to culture bacteria?

2) When culturing bacteria, why should you not incubate the cultures at a temperature no higher than 25°C?

Answer 7

1)
> as colonies on an agar plate
> in a nutrient broth solution

2) culturing bacteria in temperatures no higher than 25°C avoids growing pathogens, such as bacteria and fungi, that are harmful to humans

Question 8

how big are animal cells and plant cells?

Answer 8

animals - between 0.01mm-0.05mm

plants - between 0.01mm-0.10mm

Question 9

name the 5 main organelles of animal cells and their function.

Answer 9

cytoplasm -
>jelly-like material that contains dissolved nutrients, salts and organelles
>where many of the chemical reactions happen.

nucleus -
contains genetic material, including DNA, which controls the cell’s activities

cell membrane -
controls the movement of substances in and out of the cell- it is permeable to some substances but not others

mitochondria -
where aerobic respiration occurs

ribosomes -
where protein synthesis occurs

Question 10

name the functions of the 3 plant-only organelles.

Answer 10

chloroplast -
>where photosynthesis occurs
> contains green pigment, chlorophyll, which absorbs light energy for photosynthesis

cell wall -
made from cellulose which strengthens the cell and supports the plant

permanent vacuole -
filled with cell sap to help keep the cell turgid

Question 11

describe the differences between eukaryotes and prokaryotes.

Answer 11

eukaryotic cells-
>animal and plant cells
>have a cell membrane, cytoplasm, and genetic material enclosed in the nucleus

prokaryotic cells-
>bacterial cells
>much smaller than eukaryotes
>also have a cell membrane, cytoplasm, ribosomes and cell wall.
>genetic material isn’t enclosed in a nucleus, but a single DNA loop
>contain one or more plasmids (small rings of DNA)

Question 12

explain how sperm cells are specialised.

Answer 12

sperm -
>the tail enables the sperm to swim
>the head contains the genetic material for fertilisation
>the acrosome in the head contains enzymes so that the sperm can penetrate an egg,
>the middle piece is packed with mitochondria to release energy needed to swim and fertilise the egg

Question 13

explain how nerve cells are specialised.

Answer 13

nerve -
>the cell is extended so that nerves can run to and from different parts of the body to the central nervous system
>the cell has extensions and branches so that it can communicate with other nerve cells or muscles or glands
>the nerve cell is covered with a fatty sheath, which insulates the nerve cell and speeds up the nerve impulse

Question 14

explain how muscle cells are specialised.

Answer 14

muscle -
>contain filaments of protein that slide over each other to cause muscle contraction
>the arrangement of these filaments causes the banded appearance of heart muscle and skeletal muscle
>they contain many well-developed mitochondria to provide the energy for muscle contraction
>in skeletal muscle, the cells merge so that the muscle fibres contract in unison

Question 15

explain how root hair cells are specialised.

Answer 15

root hair -
>large surface area to provide contact with soil water
>thin wall to not restrict the movement of water

Question 16

explain how phloem cells are specialised.

Answer 16

phloem -
>dissolved sugars and amino acids can be transported both up and down the stem
>companion cells, adjacent to the sieve tubes provide energy required to transport substances in the phloem.

Question 17

explain how xylem cells are specialised.

Answer 17

xylem -
>there are no top and bottom walls between xylem vessels so there is a continuous column of water running through them
>their walls become thickened and woody to therefore support the plant

Question 18

what is cell differentiation and why is it important?

Answer 18

the process by which a cell changes to become specialised

allows them to perform specific functions as the organism develops

Question 19

how do cells differentiate?

Answer 19

develop a structure and composition of subcellular structures which enable them them to carry out their specific functions

Question 20

how does bacteria multiply?

Answer 20

binary fission (a type of simple cell division)

1) genetic material of the bacteria is replicated and the overall size of the bacteria increases
2) circular DNAs move to each end of the cell
3) the cytoplasm then divides and new cell walls form around both daughter cells

with enough nutrients and an ideal temperature, bacteria can multiply once every 20 minutes.

Question 21

why and how are bacteria grown in labs?

Answer 21

to investigate the effect of disinfectant and antibiotics by using cultures of bacteria grown in labs

they require an adequate supply of nutrients (carbs, proteins, minerals, vitamins) and a temperature no higher than 25° or else harmful pathogens can grow

Question 22

why are uncontaminated cultures vital and what are some aseptic techniques?

Answer 22

> the presence of competing species can affect the growth of cultures, as well as the validity of any study performed on them

> work in front of a lit Bunsen burner to create a convection current which prevents contamination of microorganisms in the air

> pour hot agar jelly in a steriliser Petri dish to kill microorganisms that could contaminate the experiment

> passing an inoculating loop through a flame and transferring bacteria to the culture to kill microorganisms on the loop

> slightly opening the petri dish as it faces a Bunsen burner to decrease the risk of contamination

> taping the side of the Petri dish and storing it upside down to prevent drops of condensation dropping onto the surface of the agar

Question 23

what is an inhibition zone and how do you calculate it?

how do you work out the amount of bacteria in a population?

Answer 23

> the area of the incubation zone around a substance determines how effective it is = πr²

> use the mean division time and how long a bacteria has been dividing for to see how many times it has divided. then do 2 to the power of however many times it has divided

Question 24

what are chromosomes and how many are in the body?

Answer 24

> structures made from DNA molecules that are contained in the nucleus of a cell and carry a large number of genes

> there are 23 pairs of chromosomes in the body

Question 25

what are the definitions of the cell cycle and mitosis?

Answer 25

**cell cycle** is a series of events that a cell goes through when it grows and divides **mitosis** is a type of cell division that results in two that are identical to the parent cells

Question 26

what happens during the cell cycle?

Answer 26

1)before division, the cell grows and gains more organelles 2)DNA synthesis occurs (chromosomes become double stranded as the genetic material of the cell is doubled) 3)DNA replicates to form two copies of each chromosome

Question 27

what happens during mitosis and how is it important?

Answer 27

1)the DNA replicates to form two copies of each chromosome in a cell 2)all the chromosomes line up on the equator of the cell 3)each set of chromosome is pulled to each end of the cell and the nucleus divides. 4)finally the cytoplasm and cell membranes divide to form two identical daughter cells. >Cell division by mitosis is important in the growth and development of multicellular organisms.

Question 28

what is a stem cell and what are they capable of?

Answer 28

>cells that have not undergone differentiation, meaning its undifferentiated and not yet become specialised. >they are capable of dividing/giving rise to other cells of the same type from which certain other types cells can arise from differentiation >stem cells can be used as treatment for diseases such as diabetes and paralysis

Question 29

what are embryonic stem cells?

Answer 29

Stem cells from human embryos which can be cloned and made to differentiate into most different types of human cells.

Question 30

what are adult stem cells?

Answer 30

stem cells from adult bone marrow which can form many, but limited, types of cells which are related to them such as blood cells.

Question 31

explain meristematic stem cells

Answer 31

>regions in plants that are going through mitosis are known as meristems, they are mainly located on the tip of the shoot and root >cells of the meristem can differentiate to produce all types of plant cells at any time during the life of the plant

Question 32

what is the method for therapeutic cloning?

Answer 32

1) remove the nucleus of a donor's egg cell 2) transfer the nucleus of the patient to the donor's egg cell, stimulating it to divide 3) the cells divide and form an embryo 4) the cell are then removed after 4-5 days to be cultured for therapeutic use

Question 33

1)explain the results of therapeutic cloning 2)and why this process has potential to be helpful

Answer 33

1)in therapeutic cloning, an embryo is produced with the same genes as the patient. 2)Stem cells from the embryo wouldn't be rejected by the patient’s body so the cells could used for medical treatment

Question 34

what are the disadvantages of therapeutic cloning?

Answer 34

1) the stem cells can be infected with viruses which can spread to the patient if used 2) embryonic stem cells cause many ethical problems

Question 35

explain cloning in plants.

Answer 35

>stem cells from meristems can be removed from a plant >these stems cells are cultured in a lab to stimulate growth and division so that they grow up to become a clone of the original plant >this is quick and economically beneficial

Question 36

what is the purpose of cloning plants?

Answer 36

1) clone rare species to protect them from extinction 2) crops with disease resistance (or other beneficial genes) can be cloned to produce a large number of identical plants for farmers

Question 37

what is diffusion?

Answer 37

>the movement of the particles >of any substance in solution, or particles of a gas, >resulting in a net movement from an area of higher concentration to an area of lower concentration >in and out of cells through the cell membrane

Question 38

give examples of diffusion

Answer 38

>oxygen and carbon dioxide in gas exchange >urea from cells into the blood plasma for excretion in the kidney

Question 39

what factors affect diffusion? explain how?

Answer 39

>the difference in concentrations - the greater the difference in concentration, the quicker the rate of diffusion. >the temperature - the higher the temperature, the more kinetic energy the particles will have, so they will move and mix quicker >the surface area of the membrane - the greater the surface area, the faster the rate of diffusion

Question 40

why can single-cell organisms rely on diffusion

Answer 40

>single-celled organisms have a relatively large surface area to volume ratio >this allows a sufficient transport of molecules into and out of the cell to meet the needs of the organism

Question 41

how do you calculate the surface area to volume ratio?

Answer 41

cells can be modelled as cubes 1) work out the volume of the cube (depth x height x width) 2) work out the surface area of the cube (area of one face x 6) 3) put them in a ratio e.g.: a cube with a depth and height of 1 would have a volume of 1 the surface area would be 6 (one of the faces would have an area of 1, multiply it by the 6 faces to get a total surface area of 6) put the two into a ratio: 6:1

Question 42

what is the need for exchange surfaces and a transport system in multicellular organisms in terms of surface area to volume ratio?

Answer 42

>multicellular organisms have a smaller surface area to volume ratio >and so it's be more difficult to transport substance around the cells >exchange surfaces allow substances to move in and out of cells

Question 43

How is the small intestine adapted for exchanging materials?

Answer 43

>villi are found in the small intestine >and they increase the surface area of the intestines to allow digested food to be efficiently absorbed into the bloodstream and delivered to cells around the body. >the small intestine has a large network of capillaries so that nutrients, which have been absorbed by the small intestine, can be carried away

Question 44

How are the lungs adapted for exchanging materials?

Answer 44

>many alveoli are present in the lungs that further increases surface area >alveolar walls are also one cell thick, providing gases with a short diffusion distance >the moist walls dissolve gases and helps them pass across the gas exchange surface

Question 45

How are gills adapted for exchanging materials?

Answer 45

>gills have a large surface area >and a good blood supply, for efficient gas exchange to happen in water >water that flows over the gills flows in the opposite direction to the blood >this is called counter current flow which maximises the extraction of oxygen from the water

Question 46

How are roots adapted for exchanging materials?

Answer 46

>they have root hair cells which have long thin projections that stick out into the soil >this massively increases the surface area of the root and allows it to absorb more water and mineral ions

Question 47

What is osmosis?

Answer 47

>the movement/diffusion of water from a dilute solution to a concentrated solution >through a partially permeable membrane

Question 48

what is active transport?

Answer 48

>the movement of substances from a dilute solution to a more concentrated solution, against the concentration gradient >this requires energy from respiration

Question 49

when is active transport used and why?

Answer 49

>to allow mineral ions to be absorbed into plant root hairs from dilute solutions in the soil >plants need ions for healthy growth >to allow sugar molecules to be absorbed from the lower concentrations in the gut to the blood which has a higher sugar concentration >sugar molecules are used for cell respiration