Unit 1 - Cell Biology Flashcards
What are the two types of cells?
● Prokaryotic (bacteria)
● Eukaryotic (plant and animal)
What are the differences between eukaryotic and
prokaryotic cells?
Prokaryotic cells are much smaller than
eukaryotic cells.
Eukaryotic cells contain membrane
bound-organelles and a nucleus containing
genetic material, while prokaryotes do not
What is the prokaryotic cell wall composed of?
Peptidoglycan
How is genetic information stored in a
prokaryotic cell?
Found free within the cytoplasm as:
● Chromosomal DNA (single large loop of circular DNA)
● Plasmid DNA
What are plasmids?
● Small, circular loops of DNA found free in the
cytoplasm and separate from the main DNA.
● Carry genes that provide genetic advantages
e.g. antibiotic resistanc
What is order of magnitude?
A power to the base 10 used to quantify
and compare size.
What is a micrometre (µm)?
1 × 10^-6 metres
What is a nanometre (nm)?
1 × 10^-9 metres
List the components of both plant and
animal cells (5)
● Nucleus
● Cytoplasm
● Cell membrane
● Mitochondria
● Ribosomes
List the additional cell components found
in plant cells (3)
● Chloroplasts
● Permanent vacuole
● Cell wall
Other than storing genetic information,
what is the function of the nucleus?
Controls cellular activities
Describe the structure of the cytoplasm
● Fluid component of the cell.
● Contains organelles, enzymes and dissolved
ions and nutrients.
What is the function of the cytoplasm?
Site of cellular reactions e.g. first stage of respiration.
Transport medium.
What is the function of the cell membrane?
Controls the entry and exit of materials
into and out of the cell.
What is the function of the mitochondria?
Site of later stages of aerobic respiration
in which ATP is produced
What is the function of the ribosomes?
Joins amino acids in a specific order
during translation for the synthesis of
proteins.
What is the plant cell wall made of?
Cellulose
What is the function of the plant cell wall?
● Provides strength.
● Prevents the cell bursting when water
enters by osmosis
What does the permanent vacuole contain?
Cell sap (a solution of salts, sugars and
organic acids).
What is the function of the permanent vacuole?
Supports the cell, maintaining its
turgidity.
What is the function of chloroplasts?
Site of photosynthesis
Describe how sperm cells in animals are adapted to
their function
● Haploid nucleus contains genetic information.
● Tail enables movement.
● Mitochondria provide energy for tail movement.
● Acrosome contains enzymes that digest the egg cell
membrane.
Describe how nerve cells in animals are adapted to
their function
● Long axon allows electrical impulses to be transmitted all over
the body from the central nervous system.
● Dendrites from the cell body connect to and receive impulses
from other nerve cells, muscles and glands.
● Myelin sheath insulates the axon and speeds up the
transmission of impulses along the nerve cell.
Describe how muscle cells are adapted to their
function
● Arrangement of protein filaments allows them to
slide over each other to produce muscle contraction.
● Mitochondria to provide energy for muscle
contraction.
● Merged cells in skeletal muscle allow muscle fibre
contraction in unison.
Describe how root hair cells in plants are adapted to
their function
● Large surface area to absorb nutrients and
water from surrounding soil.
● Thin walls that do not restrict water
absorption.
Describe how xylem cells in plants are adapted to
their function
● No upper or lower margins between cells
to provide a continuous route for water to flow.
● Thick, woody side walls strengthen their
structure and prevent collapse.
Describe how phloem cells in plants are adapted to
their function
● Sieve plates let dissolved amino acids and
sugars be transported up and down the stem.
● Companion cells provide energy needed for
active transport of substances along the
phloem.
What is cell differentiation?
The process by which cells become
specialised.
Why is cell differentiation important?
Allows production of different tissues and
organs that perform various vital
functions in the human body.
At what point in their life cycle do most animal cells
differentiate?
Early in their life cycle
For how long do plant cells retain the ability to
differentiate?
Throughout their entire life cycle
What is the purpose of cell division in mature
animals?
Repair and replacement of cells
What changes does a cell go through as it
differentiates?
Becomes specialised through acquisition
of different sub-cellular structures to
enable a specific function to be
performed by the cell.
Define magnification
The number of times bigger an image
appears compared to the size of the real
object.
How does a light microscope work?
Passes a beam of light through a specimen
which travels through the eyepiece lens,
allowing the specimen to be observed.
What are the advantages of light microscopes? (4)
● Inexpensive
● Easy to use
● Portable
● Observe both dead and living specimens
What is the disadvantage of light microscopes?
Limited resolution
How does an electron microscope work?
It uses a beam of electrons which are
focused using magnets. The electrons hit
a fluorescent screen which emits visible
light, producing an image.
What is the advantage of electron microscopes?
Greater magnification and resolution.
Why do electron microscopes have a greater
magnification and resolution?
They use a beam of electrons which has
a shorter wavelength than photons of
light.
How have electron microscopes enabled scientists
to develop their understanding of cells?
● Allow small sub-cellular structures (e.g. mitochondria,
ribosomes) to be observed in detail.
● Enable scientists to develop more accurate
explanations about how cell structure relates to
function.
What are the disadvantages of electron
microscopes? (4)
● Expensive
● Large so less portable
● Require training to use
● Only dead specimens can be observed
How can the magnification of an image be
calculated?
magnification =
size of image / size of real object
What nutrients make up a nutrient broth solution?
All nutrients required for bacteria to grow
including nitrogen for protein synthesis,
carbohydrates for energy and other
minerals.
Describe the preparation of an uncontaminated
culture using aseptic technique
- Use pre-sterilised plastic Petri dishes or sterilise glass Petri dishes and agar
gel before using with an autoclave. - Pour the sterile agar gel into the Petri dish and allow time to set.
- Sterilise the inoculating loop by passing it through a Bunsen burner flame.
- Dip the inoculating loop into the solution of microorganisms and make streaks
with the loop on the surface of the agar. - Put the lid on the Petri dish and secure it with tape. Label accordingly then
turn and store upside down. - Incubate the culture at 25oC in school laboratories.
Why must Petri dishes and culture media before
sterilised before use?
To kill any bacteria already present.
Why must inoculating loops be sterilised by passing
them through Bunsen burner flame?
To kill any bacteria present on the
inoculating loop.
Why must the Petri dish lid be secured with adhesive
tape and the whole dish stored upside down?
Stops bacteria in the air contaminating the culture.
The lid is not fully sealed to prevent the growth of
anaerobic bacteria in a lack of oxygen.
Upside down to prevent condensation from forming
and dripping down onto the colonies.
What is the formula used to calculate cross-sectional
area of a bacterial colony or clear area around a
bacterial colony?
πr2
= 3.14
r = radius (diameter/2)
Why are cultures incubated at 25oC in school
laboratories?
Harmful pathogens are less likely to to
grow at this temperature.
How is the number of bacteria in a population after a
certain time calculated from the mean division time?
- Calculate the number of times the bacteria will divide in the given time period
from the mean division time. - Use the following equation to calculate the number of bacteria:
Number of bacteria in population at end of time period = number of bacteria at
the beginning of the time period x 2^number of divisions in the time period.
Express the answer in standard form if possible.
What are chromosomes made up of?
Chromosomes consist of DNA molecules
combined with proteins. They contain
genes which provide the instructions for
protein synthesis.
What is a gene?
A section of DNA which codes for a
protein.
How many chromosomes are found in the
nucleus of human body cells?
46
How many chromosomes are found in the nucleus of
gametes?
23
How are chromosomes arranged in the nucleus
of a body cell?
Arranged in pairs - 46 chromosomes
form 23 pairs.
What are the three main stages of the cell
cycle?
- Replication of DNA and synthesis of
organelles - Mitosis
- Division of cell
Why is mitosis important?
● Produces identical cells which all have the
same genetic information.
● Produces additional cells for growth and
repair.
Describe the first stage of the cell cycle
Longest stage - cells grow and increase
in mass, replicate DNA and synthesise
more organelles (eg. mitochondria,
ribosomes).
Describe the second stage of the cell cycle
Each chromosome in a pair is pulled to
opposite poles of the cell, then the nucleus
divides.
Describe the third stage of the cell cycle
The cytoplasm and cell membrane divide -
two identical daughter cells are produced.
What is a stem cell?
An unspecialised cell which is capable of
differentiating into other cell types and of
self-renewal.
What is the function of stem cells in embryos?
Embryonic stem cells can replicate themselves and
differentiate into many other types of cells.
Embryonic stem cells may be able to treat conditions
such as paralysis and diabetes by dividing to replace
damaged cells.
What is the function of stem cells in adult bone
marrow?
Adult stem cells can differentiate into several cell
types to replace dead or damaged tissues. For
example, bone marrow stem cells can form many
different types of blood cell.
What is the function of stem cells in plant
meristems?
Meristem stem cells retain the ability to
differentiate into any type of plant cell throughout
their lifespan - they can differentiate into any cell
which is required by the plant.
What is therapeutic cloning?
A cloning method where an embryo is produced
with the same genetic makeup as the patient.
The stem cells which originate from the embryo
will not be rejected by the patient’s immune
system, so can be used to treat certain medical
conditions.
What are the advantages of cloning plants using
meristem stem cells?
● Can prevent rare plants from becoming extinct.
● Can produce large numbers of plants with a
favourable characteristic.
● Can produce identical plants for research.
What are issues are associated with the use of
stem cells?
● Many embryonic stem cells are sourced from aborted embryos -
some people have an ethical/religious objection.
● Development of stem cell therapies is slow, expensive and difficult.
● Adult stem cells infected with viruses could transfer infections to
patients.
● If donor stem cells do not have a similar genetic makeup to the
patient, an immune response could be triggered.
What is diffusion?
The net movement of particles from an
area of higher concentration to an area of
lower concentration.
What three main factors affect the rate of
diffusion?
● Concentration gradient - larger gradient, faster
diffusion.
● Temperature - higher temperature, faster diffusion.
● Surface area - larger surface area, faster diffusion.
Give examples of substances transported by diffusion in
the lungs and the kidney
● Lungs: oxygen diffuses into the blood from the lungs
and carbon dioxide diffuses into the lungs from the
blood, both down their concentration gradient.
● Kidney: urea diffuses from cells into blood plasma so
it can be excreted in urine.
How are single-celled organisms adapted for
diffusion?
They have a large surface area to volume
ratio - maximises the rate of diffusion of
molecules to meet the organism’s needs.
How is surface area to volume ratio calculated?
Surface Area = Number of Sides x (Side
Length x Side Width)
Volume = Length x Width x Depth
Ratio = Surface Area:Volume
What four factors increase the effectiveness of a
gas exchange surface?
● Large surface area
● Thin membrane (short diffusion path)
● Efficient blood supply (animals)
● Ventilation (animals)
What is osmosis?
The movement of water from a dilute solution
to a concentrated solution through a partially
permeable membrane.
What is meant when a solution is isotonic to a cell?
The concentrations of the external and
internal (inside cell) solutions are the same.
What is meant when a solution is hypertonic to a
cell?
The concentration of the external solution is
higher than that of the internal solution (inside
cell).
What is meant when a solution is hypotonic to a
cell?
The concentration of the external solution is
lower than that of internal solution (inside
cell).
What may happen when an animal cell is placed
in a very hypotonic solution?
Water moves into the cell, causing it to burst
What may happen when an animal cell is placed
in a very hypertonic solution?
Water moves out of the cell, causing it to shrivel
up.
How do plant leaves and stems remain rigid?
Turgor pressure - water moves in by osmosis,
causing the vacuole to swell and the cytoplasm
to press against the cell wall.
What may happen when a plant cell is placed in a
very hypertonic solution?
Water moves out of the cell by osmosis and the
vacuole and cytoplasm decrease in size. The cell
membrane may pull away from the cell wall,
causing the cell to become plasmolysed.
What is active transport?
The movement of molecules from a more
dilute solution to a more concentrated solution
against a concentration gradient, using energy
from respiration.
How do plant root hair cells use active transport?
Root hair cells use active transport to take
up mineral ions from a more dilute solution in
soils. Ions such as magnesium and nitrates
are required for healthy growth.
How is active transport used to absorb the
products of digestion?
Active transport is used to transport glucose from a
lower concentration in the gut to a higher
concentration in the blood. Glucose is then
transported to the tissues where it can be used in
respiration.
