Cell biology Flashcards
Features of an animal cell
- nucleus and genetic material (usually DNA)
- cytoplasm
- ribosomes (rough endoplastic reticulum)
- cell membrane
- mitochondria
cell membrane
- exterior of all protoplasm
- very thin layer
- freely permeable to water and gases only
- selectively permeable to other molecules
cytoplasm
- a gel-like substance composed of water and dissolved solutes
- supports organelles
- site of many chemical reactions, including anaerobic respiration
- consistency of egg-white
- up to 80% water, remained mainly protein
- often contains grains of stored food
nucleus
- stores and passes on cell information
- contains many long strands of DNA
Ribosomes
- Invisible (20nm) without the electron microscople.
- protein synthesis: assemble amino acids into proteins, each different according to purpose (instructons for assembly are from the nucleus).
Typical plant cell
- cell membrane
- chloroplast
- nucleus
- cell wall (made from cellulose)
- ribosomes on rough endoplasmic reticulum
- mitochondrion
- cytoplasm
- large, cell sap, permanent vacuole
Why are animal and plant cells both eukaryotic cells?
Their genetic material is enclosed in a nucleus.
What does a typical plant cell have which a typical animal cell doesn’t?
- cell wall
- large, cell sap, permanent vacuole
- chloroplasts
What is a defining feature of prokaryotic cells?
Their genetic material is not enclosed within a nucleus, it is found as a single loop of DNA within the cytoplasm.
As well as the single loop of DNA found in the cytoplasm of prokaryotic cells, what may also be present?
Additional smaller, circular pieces of DNA called plasmids.
The cell membrane of all prokaryotic cells are surrounded by
a cell wall (usually made from a substance called peptidoglycan)
Size of many prokaryotic cells.
1 micrometre
Are eukaryotic cells bigger than prokaryotic cells?
Yes.
Prokaryotic cells
- cell membrane
- circular loop of DNA
- plasmid
- ribosomes
- cytoplasm
- cell wall made from peptidoglycan
Many subcellular structures in eukaryotic cells are _____ than prokaryotic cells.
bigger
order of magnitude
The difference in size calculated by the factor of 10.
Why do prokaryotic cells not contain mitochondria?
Prokaryotic cells do not contain membrane-bound organelles, therefore do not contain mitochondria.
organelles
subcellular ‘compartments’ where specific processes take place within the cell.
What organelles in an animal cell are not visible to a light microscope but are only visible to electron microscopes?
mitochondrion and ribosomes
cell wall
- made up of cellulose (polymer of glucose)
- freely permeable to all kinds of molecules
- supports and protects the cell
- osmoregulates by resisting the entry of excess water into cell
chloroplast
- large bodies containing chlorophyll
- chlorophyll converts sunlight energy into chemical energy (ATP) for photosynthesis.
large, cell sap, permanent vacuole
- contains cell sap; a solution of sugars and salts dissolved in water
- important for keeping the cells rigid to support the plant
- used for storage of certain materials eg: food
mitochondria
- site of most of the reactions involved in aerobic respiration, where energy is released to fuel cellular processes
- cells with high rates of metabolism (carrying out many different cell reactions) have significantly higher numbers of mitochondria than cells with fewer reactions taking place.
A specialised cell
-a cell that has a particular structure and composition of subcellular structures
Structural differences between different types of cells enable them to
perform specific functions within the organism.
cells specialise by undergoing a process called
differentiation
The nerve cell function
The conduction of impulses
Adaptations of a nerve cell
- have an elongated structure which allows them to coordinate information from the brain and spinal cord with the rest of the body.
- has a cell body where most of the cellular structures are located and most protein synthesis occurs
- extensions of the cytoplasm from the cell body form dendrites (which receive signals) and axons (which transmit signals), allowing the neurone to communicate with other nerve cells, muscles and glands.
- the axon (the main extension of cytoplasm away from the cell body) is covered with a fatty sheath, which speeds up nerve impulses. Axons can be up to 1m long in some animals.
components of a nerve cell
- cell body
- ribosome
- dendrites
- cell membrane
- nucleus
- cytoplasm
- axon
- myelin sheath (made from schwann cells)
- nerve ending
components of muscle cells
- protein filament
- cell membrane
- nuclei
- mitochondria
- ribosomes
Function of muscle cells
contraction for movement
Adaptations of muscle cells
- contain layers of fibres which allow them to contract
- there are three different types of muscle in animals: skeletal, smooth and cardiac (heart).
- all muscle cells have protein filaments in them. These layers can slide over each other causing muscle contraction
- muscle cells have a high density of mitochondria to provide sufficient energy (via respiration) for muscle contraction.
- skeletal muscle cells fuse together during development to form multinucleated cells that contract in unison.
Adaptations of a muscle cell
- contain layers of fibres which allow them to contract
- there are three different types of muscle in animals: skeletal, smooth and cardiac
- All muscle cells have layers of protein filaments in them. These layers can slide over each other causing muscle contraction
- Muscle cells have a high density of mitochondria to provide sufficient energy (via respiration) for muscle contraction
- Skeletal muscle cells fuse together during development to form multinucleated cells that contract in unison.
components of sperm cells
- head
- acrosome
- cell membrane
- nucleus
- mid-piece
- cytoplasm
- mitochondria
- tail/flagellum
Function of sperm cells
reproduction (pass on fathers genes)
Adaptations of sperm cells
- the head contains a nucleus which contains half the normal number of chromosomes (haploid, no chromosome pairs)
- the acrosome in the head contains the digestive enzymes that can break down the outer layer of an egg cell so that the haploid nucleus can enter to fuse with the egg’s nucleus
- The mid-piece is packed with mitochondria to release energy (via respiration) for the tail
- The tail rotates, propelling the sperm cell forwards (allowing it to move/swim)
root hair cell components
- ribosomes
- mitochondrion
- nucleus
- cytoplasm
- cell membrane
- cell wall
- root hair
- vacuole
function of root hair cell
absorption of water and mineral ions from the soil
Adaptations of root hair cell
- root hair to increase surface area (SA) so the rate of water uptake by osmosis is greater (can absorb more water and ions than if SA were lower)
- Thinner walls than other plant cells so that water can move through easily (due to shorter diffusion distance)
- Permanent vacuole contains cell sap which is more concentrated than soil water, maintaining a water potential gradient
- Mitochondria for active transport of mineral ions
- chloroplasts are not found in these cells- there is no light for photosynthesis underground
function of a xylem vessel
- it is a transport tissue for water and dissolved ions
Adaptations of xylem cells
- no top and bottom walls between cells to form continuous hollow tubes through which water is drawn upwards towards the leaves by transpiration
- cells are essentially dead, without organelles or cytoplasm, to allow free passage of water
- outer walls are thickened with a substance called lignin, strengthening the tubes which helps support the plant.
- xylem cells lose their top and bottom walls to form a continuous tube through which water moves through from the roots to the leaves.
Phloem cells function
- transport of dissolved sugars and amino acids
Phloem cells adaptations
- Phloem cells form tubes similar to xylem vessels, except the cells still retain some subcellular structures and are therefore living.
- made of living cells (as opposed to xylem vessels which are made of dead cells) which are supported by companion cells.
- cells are joined end-to-end and contain holes in the end cell walls (sieve plates)forming tubes which allow sugars and amino acids to flow easily through (by translocation).
- cells also have very few subcellular structures to aid the flow of materials.
cell differentiation
The process by which a cell changes to become specialised
cells which have not differentiated are
unspecialised
As an organism develops, cells
differentiate to form different types of cells
What is the genetic information like in the cells of a multicellular organism?
Almost all of the cells in a multicellular organism contain the same genetic information (the same genes or alleles), but depending on the role one particular cell needs to have, only some of the total sum of genes in a particular cell are used to control its development.
When a cell differentiates, what does it develop?
a structure and composition of subcellular structures which enables it to carry out a certain function.
To form a nerve cell, what must an undifferentiated cell do?
The cytoplasm and cell membrane of an undifferentiated cell must elongate to form connections over large distances.
Meiosis
- Cells in reproductive organs divide by meiosis to form gametes (sex cells)
- The number of chromosomes must be halved when the gametes are formed
- Otherwise, there would be double the number of chromosomes after they join at fertilisation in the zygote (fertilized egg)
- This halving occurs during meiosis, and so it is described as a reduction division in which the chromosome number is halved from diploid to haploid, resulting in genetically different cells
- It starts with chromosomes doubling themselves as in mitosis and lining up in the centre of the cell
- After this has happened the cells divide twice so that only one copy of each chromosome passes to each gamete
- We describe gametes as being haploid – having half the normal number of chromosomes
- Because of this double division, meiosis produces four haploid cells
Mitosis occurs in
somatic cells
resolution
It refers to the smallest non-zero value that can be detected/measured using a measuring instrument.
Examples of the resolution of different instruments
eg: thermometer- 1 degrees Celsius, Protractor- 1 degree, ruler- 1mm
digital ammeter- 0.01 A
digital voltmeter- 0.01 V
chemical balance - 0.01 g)
Advantage of a higher resolution
The higher the resolution, the lower the percentage uncertainty- greater degree of accuracy.
standard deviation
the degree/value that is away from the mean
error bars
show the deviation above the mean
Light microscope
- low resolution
- low magnification
- certain subcellular structures/ organelles (mitochondria, ribosomes) cannot be detected.
electR^2on microscope
- high resolution
- subcellular structures can be detected (ribosomes, mitochondrion)
- high magnification
REQUIRED PRACTICAL
1,Using a dropper, allow a drop of water onto a microscope slide
2,Using a scalpel and thereafter a pair of tweezers, remove a sample of epidermal cells from an onion
3,Carefully place the samples onto the microscope slide and add a drop or two of iodine to stain the sample.
4, Place a coverslip over the sample-to prevent any air bubbles (watertight)
5, Use low magnification/coarse adjustment first and bring the sample into focus.
6, Higher magnification/fine adjustment can be used to observe subcellular structures/organelles.
7, Using a pencil, draw your observations and give the sample a title.
magnification =
image size/ real size
Differences between light and electron microscope
Light: -low resolution -low magnification -subcellular structures Electron: -high resolution -high magnification
stem cells
Cells that have become specialised for a specific function
spErM^2
- head of cell contains enzymes to digest egg cell membrane
- many mitochondria releases energy
- male sex cell/gamete
neRvES
- electrical impulses
- rapid signalling
MusCle
- mitochondria release energy
- muscular contraction
root hair cell
- increase SA:VR
- increases rate at which osmosis takes place.
Differences between eukaryotic and prokaryotic cells
- eukaryotic are much larger than prokaryotic which are much smaller
- prokaryotic have a genetic strand
- bacteria contains plasmids
How do bacteria divide?
By binary fission
number =
total/division time
-then 2 to the power of answer to find the total amount of bacteria
What do most animal cells have?
- a nucleus
- a cytoplasm
- a cell membrane
- mitochondria
- ribosomes
What do plant cells often have? (in addition to the parts found in animal cells)?
- chloroplasts
- a permanent vacuole filled with cell sap
- also have a cell wall made of cellulose, which strengthens the cell
What is the genetic material in a prokaryotic cell?
The genetic material is not enclosed in a nucleus. It is a single DNA loop and there may be one or more small rings of DNA called plasmids.
How much bigger is every order of magnitude?
10x greater than the one before.
What does cellulose do?
It strengthens the cell wall.
Phloem
transport soluble food particles throughout the plant. 2 directional flow. Living.
Xylem
transport water and mineral ions from roots to leaf cells. 1 direction. Non living
Prokaryotic (bacteria)
- no nucleus, has DNA strand
- bacteria contain plasmids
- bacteria carry out binary fission
What happens to cells as an organism develops?
Cells differentiate to form different types of cells.
When do most types of animal cells differentiate?
At an early stage.
When do many types of plant cells differentiate?
They retain the ability to differentiate throughout their life.
What cell division occurs in mature animals?
Cell division is mainly restricted to repair and replacement.
How does a cell become specialised?
As a cell differentiates, it acquires different sub-cellular structures to enable it to carry out a certain function. It has become a specialised cell.
What is a defining feature of eukaryotic cells?
Their genetic material (DNA) is enclosed within a nucleus
What is the size of eukaryotes?
Usually between 10 and 100 micrometres
What is the size of many prokaryotic cells?
1 micrometer
cells that have not differentiated are
unspecialised
magnification
image size/ real size
Where can bacteria be grown?
In a nutrient broth solution or as colonies on an agar gel plate.
What happens during binary fission?
A copy of each piece of circular DNA moves to each end of the cell before the cytoplasm divides, and new cell walls form around each daughter cell.
In the right conditions. how quickly do some species of bacteria multiply?
They can multiply as much as once every 20 minutes.
Why is the timing for optimal binary fission ideal?
Large cultures of bacteria for study can be grown in relatively short periods of time.
How can bacteria multiply quickly?
Bacteria require an adequate supply of nutrients (carbohydrates, proteins, minerals and vitamins) and an appropriate temperature (which varies o the species being grown).
Temperatures for growing bacterial cultures in a lab
- warmer temperatures promote faster growth
- Above 25 degrees C, more harmful pathogens are likely to grow.
What is the maximum allowed temperature for growing bacterial cultures in a school lab?
25 degrees Celsius.
uncontaminated culture preparation steps with explanations
1, pre-inoculation
petri dish and agar are sterilised before use to kill unwanted bacteria
inoculating loop passed through flame/ sterile swab to sterilise/kill other bacteria
2, Inoculation
The loop/swab used to spread/streak bacterium onto agar
The lid of the petri dish opened as little as possible to prevent microbes from the air entering
3, Post inoculation
It is sealed with tape to prevent microbes from the air entering.
Incubate to allow growth of the bacteria.
The cultures should not be incubated above 25 degrees C in a school laboratory - this restricts the growth of harmful pathogens (which are more likely to grow at higher temperatures).
What can the effectiveness of different antibiotics, antiseptics or disinefectants be determined by?
The area of inhibition zone
What is the inhibition zone?
An area where no bacterial growth has occured; the larger the zone, the more effective the substance tested is against the bacteria.
How do you calculate the area of the inhibition zone?
pi x r^2
What is the mean division time of bacteria?
The average amount of time it takes for a bacterial cell in a population to divide.
number of bacteria =
2 ^ time dividing/ mean division time
What does the nucleus of a cell contain?
Chromosomes made of DNA molecules
What does each chromosome carry?
A large number of genes
In body cells, how are chromosomes normally found?
In pairs
What are chromosomes made from?
Highly coiled strands of relatively long DNA. Each chromosome is made from one DNA molecule.
How are chromosomes normally found in the body cells of diploid organisms?
In pairs
Why are chromosomes found in pairs in body cells?
One chromosome from each pair is inherited from the mother, the other from the father
What needs to happen to a cell before it can divide?
Its genetic material needs to be doubled
What happens during the growth phase of the cell cycle?
The genetic material of the cell (chromosomes) is doubled and the number of subcellular structures (such as ribosomes and mitochondria) also increases.
What happens after the growth phase of the cell cycle?
Two copies of each chromosome are produced which initially remain attatched to each other with each strand called a chromatid. The chromatids will eventually be divided between the two genetically identical daughter cells that form from the dividing cell.
Describe the process of mitosis
- DNA is replicated
- each chromosome has been duplicated
- the nuclear membrane breaks down
- chromosomes line up along the centre of the cell
- Once the chromatids have been separated, the cell begins to divide: cytokinesis
- Two genetically identical daughter cells are produced.
What are organisms that are made from more than one cell described as?
multicellular
Eukaryotic cells
Describes cells that contain a nucleus
Eukaryote
an organism that is made if eukaryotic cells
Why is cell division by mitosis important?
It is important in the growth and development of multicellular organisms.
Give an example of mitosis
A zygote cell divides by mitosis, with each subsequent cell dividing in the same way to form an embryo. As the embryo continues to grow in size, with the cells dividing by mitosis (and differentiating), a fetus forms.
Through what process do specialised cells form?
differentiation
What are stem cells?
A stem cell is an undifferentated cell of an organisms which is capable of dividing to give rise to many more cells of the same type (undifferentiated stem cells).
How can other cells arise from a stem cell?
Through differentiation
Embryonic stem cell
- source: on the inside layer of an embryo
- can grow into any specialised cell found in the adult organism- totipotent
- once an embryonic stem cell has differentiated into a specialised cell, it cannot turn back or turn into any other type of cell.
Adult stem cells
- found in bone marrow (skin, other organs such as the liver and brain and umbilical cord blood).
- used to repair the body when it is unjured
- can develop into the type of cell found in that location (blood adult stem cells can only develop into red or white blood cells)
- cannot turn into any cell like embryonic stem cells - multipotent
- may not be as potentially useful as embryonic stem cells
Lizard stem cells:
- They have stem cells that allow them to regenerate parts of their body
- Lizards can shed, and late regrow, their tail if seized by a predator.
Starfish stem cells
- If one leg of a starfish is severed by a predator it will grow back
Where a stem cells located in a plant?
In the meristem, where much of the plant’s growth occurs
Wher are meristems found?
In shoot tips, where they encourage the shoots to grow towards the light. They are also found in the root tips where they encourage the roots to grow downwards towards water.
Why can we take cuttings of plants?
Because the plant stem cells can differentiate into other cells throughout the mature organism’s life.
How is a plant cutting taken?
1, a small section of stem , usually with a few leaves, is removed
2, This is often dipped into rooting powder, which contains plant hormones to speed up differentiation
3, The cutting is placed directly into the soil
4, The stem cells towards the bottom of the cutting will quickly grow downwards and into root cells
5, We now have a genetically idental copy of the parent plant - a clone a little later.
Why will a plant clone not always look identical to the parent organism?
- Although there is no genetic variation, there is still environmental variation.
Meristem tissue can differentiate
into any type of plant cell, throughout the life of the plant.
What is the role of adult stem cells?
It is predominantly to replace cells lost through damage or to produce new cells for growth- although the bone marrow has to continually make new blood cells throughout life.
Importance of cloning
- much of our food that comes from plants: crops with disease resistance, is grown from clones following the cloning method
- many rare or valuable plants are grown in this way
What do many scientists think stem cell research will help?
- help treat paralysed patients by making new nerve cells to transplant into a severed spinal cord or damaged brain
- treat conditions such as diabetes to replace the cells in the body that are no longer working properly
- replace cells of the choroid in the eye to help patients see again
- replace injured or defective organs
What do many scientists think stem cell research will help?
- help treat paralysed patients by making new nerve cells to transplant into a severed spinal cord or damaged brain
- treat conditions such as diabetes to replace the cells in the body that are no longer working properly- insulin producing cells
- replace cells of the choroid in the eye to help patients see again
- replace injured or defective organs
Advantage of therapeutic cloning
Doctors can be sure that the cells will not be rejected in the way that some trnasplants are as it is using stem cells from an injured person’s own body
What are the most useful stem cells for stem cell research and why?
Embryonic stem cells because they are totipotent; they can develop into any type of cell.
How are embryonic stem cells collected?
They are often collected from waste cells in left-over umbilical cord after a mother has given birth. They are found in fertilised ova that are not selected to be put into a woman’s uterus during in vitro fertilisation (IVF).
ethical issues with embryonic stem cells
- some believe that a fertilised ovum is a life
- some believe that a fertilised ovum has rights and that its use in medical research amounts to murder
- regulations surrounding stem cell research are extremely tight and some countries forbid it completely
- using stem cells can have other problems too, like causing viral infections when infected stem cells are used.
in vitro fertilisation
A medical procedure in which ova are fertilised outside of a woman, then placed into her uterus to develop into a baby.
Diffusion
The net movement of particles from an area of higher concentration to an area of lower concentration.
Diffusion is a
passive process
What can diffuse across the cell membrane?
Oxygen and carbon dioxide can diffuse across the cell membrane during gas exchange whereas the carbohydrate starch cannot (it’s too big).
What substances can leave cells by diffusion?
Liver cells break down excess amino acids into the waste product urea which is highly toxic and must diffuse out of the cells to be excreted by the kidneys
Carbon dioxide produced by aerobic respiration must diffuse out of cells
Why does
- as the surface area increases the rate of diffusion also increases
- as there are more places for diffusion to happen faster
Adaptations of the alveoli
- ventilation moves air in and out and helps maintain a steep diffusion gradient
- conc gradient maintained in capillaries due to blood flow bringing oxygen and removing carbon dioxide
- thickness of capillary wall- capillary and alveolar wall are one cell thick, decreasing the diffusion distance
- alveoli increases surface area so diffusion occurs faster
