cell biology Flashcards
(104 cards)
1
Q
What is a cell?
A
- the basic unit of all forms of life
2
Q
What are the differences between eukaryotic cells and prokaryotic cells?
A
- prokaryotic cells are smaller
- prokaryotic cells do not have a nucleus like eukaryotic cells
- instead it contains a single DNA loop and plasmids (small rings of DNA)
- prokaryotic cells don’t have mitochondria but eukaryotic cells do
3
Q
Convert centimetres, millimetres, micrometres and nanometres
A
*1cm = 10mm
* 1mm = 1000micrometres
* 1micrometre = 1000nm
4
Q
Define a eukaryotic cell
A
- a cell that contains its genetic material (i.e. DNA) enclosed in a nucleus
5
Q
What are the sub-cellular structures in animal cells?
A
- nucleus, cytoplasm, cell membrane, mitochondria, ribosomes
6
Q
What is the function of the nucleus?
A
- contains DNA coding for a particular protein needed to build new cells
- enclosed in a nuclear membrane
7
Q
What is the function of the cytoplasm?
A
- gel-like substance where most of the chemical reactions happen
- contains enzymes that control these chemical reactions
- organelles are found in it
8
Q
What is the function of the cell membrane?
A
- holds the cell together
- controls what enters and leaves the cell
9
Q
What is the function of the mitochondria?
A
- where aerobic respiration takes place to release energy for the cell’s reactions
10
Q
What is the function of the ribosomes?
A
- site of protein synthesis
- found on the rough endoplasmic reticulum
11
Q
What additional sub cellular structures do plant cells have?
A
- chloroplasts, cell wall, vacuole
12
Q
What is the function of a cell wall?
A
- plant and algal cells have a cell wall made of cellulose
- supports and strengthens the cell
13
Q
What is the function of permanent vacuole?
A
- contains cell sap
- helps keep the plant turgid and rigid
14
Q
What is the function of chloroplasts?
A
- where photosynthesis occur
- contain chlorophyll to absorb light energy needed for photosynthesis
15
Q
What are the sub-cellular structures in bacteria?
A
- cytoplasm, cell membrane, cell wall (made of peptidogylcan), spherical nucleoid, plasmids
16
Q
What is the difference between the nucleus of a bacterial cell compared to other cells?
A
- bacterial cells don’t have a central nucleus that the genetic material is stored in
- it has a spherical nucleoid in which all the DNA is held
17
Q
Define differentiation
A
- the process by which a cell changes to become specialised
- they develop different subcellular structures and turn into different types of cells to carry out specific functions
18
Q
What is the function of a sperm cell?
A
- to fertilise an egg
- specialised for reproduction
19
Q
What are the adaptations of a sperm cell?
A
- contain half the genetic material of a normal adult cell - when fertilisation takes place, they produce a normal body cell
- long tail and streamline - allows them to swim to the egg and fertilise it
- has an acrosome which contains enzymes - allows it to digest through the cell membrane of the egg and fertilise it
- many mitochondria - provides energy for it to swim via aerobic respiration
20
Q
What is the function of a nerve cell?
A
- to carry electrical impulses around the body
- specialised for rapid signalling
21
Q
What are the adaptations of a nerve cell?
A
- long axon - allows it to carry impulses over long distances
- myelin covered axons - insulate the axon which speeds up transmission of nerve impulses
- synapses - allow it to connect to other nerve cells and carry the impulse from one cell to another
- dendrites - increase surface area so other nerve cells can connect to it
- nerve endings have many mitochondria - supply energy to make neurotransmitter
22
Q
What is the function of a muscle cell?
A
- to contract and relax to allow for movement
- specialised for contraction
23
Q
What are the adaptations of a muscle cell?
A
- contain lots of mitochondria - releases energy for muscular contraction using aerobic respiration
- have protein fibres (myosin & actin) - can change their length, allowing the cell to contract and shorten
- long - have space to contract
- can store glycogen - used in respiration
24
Q
What is the function of a root hair cell?
A
*to absorb nutrients and water from the soil
* specialised for absorbing water and minerals
25
What are the adaptations of a root hair cell?
* large surface area - allowing more water and mineral ions to be absorbed into the cell more effectively and more quickly
* lots of mitochondria - provide energy for active transport of mineral ions via cellular respiration
* large permanent vacuole - increased solute concentration inside the cell, steep concentration gradient for water to diffuse across by osmosis
26
What is the function of a xylem cell?
* to carry water and dissolved mineral ions from the roots to the leaves
27
What are the adaptations of a xylem cell?
* thick walls containing lignin (spirals) - strengthens the cell, helps to support the plant, allows it to withstand the high water pressure
* there are no end walls between cells - form hollow tubes with open ends, allows for a continuous flow of water and dissolved mineral ions to travel through these cells
* they have no nucleus, cytoplasm, vacuole or chloroplasts - more space for dissolved mineral ions and water to flow
28
What is the function of a phloem cell?
* to carry dissolved sugars ( the products of photosynthesis - glucose, sugar, amino acids) up and down the plant
* made up of vessel cells and companion cells
* specialised for transporting substances
29
What are adaptations of phloem cells?
* little subcellular structures - allows glucose to travel through
* lots of mitochondria - provides energy for the active transport and translocation of sugars up and down the plant by respiration
* sieve plates - allows dissolved sugars to travel from cell to cell, forming a tube
30
How does differentiation occur in animals?
* most types of animal cell differentiate at an early stage
* the ability to differentiate is normally lost at an early stage after they become specialised
* happens to repair or replace damaged cells
31
How does differentiation occur in plants?
* many types of plant cell retain the ability to differentiate throughout life
32
Who observed the first cells of a cork?
* Robert Hooke in 1665 using a light microscope
33
How do light microscopes work?
* has two lenses - objective and eyepiece
* objective lenses produces a magnified images, directed into the eye by the eyepiece lens
* use light and lenses to form an image of a specimen and magnify it
* let us see tissues, individual cells and large subcellular structures
* max magnification of x2000
* resolving power of 200nm
34
How do electron microscopes work?
* they use electrons to form an image - have a much smaller wavelength
* two types : scanning (SEM) that creates 3D images, lower mag, transmission (TEM) that creates 2D images, detailing organelles
* magnification up to x2,000,000
* resolving power of 10nm (SEM) and 0.2nm (TEM)
35
Evaluate the use of light microscopes and electron microscopes
* EM has much higher magnification and resolving power than a LM - can be used to study cells in much finer detail
* LM allows us to see individual cells and large sub cellular structures e.g. nuclei, whereas EM can only view dead and dry
* LM are typically cheaper than EM
* EM are large and static whereas LM are smaller and portable
36
Why did the invention of electron microscopes help develop microscopy?
* EM allow us to see in a higher magnification and resolution
* we can now see smaller sub cellular structures in finer detail
* their internal structures can be investigated now as well due to the development of technology and scientific research
37
What is the formula for magnification?
* magnification = image / real size
38
How do bacteria multiply, how often and under what conditions?
* via binary fission as often as once every 20 minutes, as long as they have enough nutrients and a suitable temperature
39
How does binary fission work?
* the circular DNA and plasmids replicate
* the cell gets bigger and the DNA strands move to opposite poles of the cell
* the cytoplasm begins to divide and new cell walls begin to form
* the cytoplasm divides and two daughter cells are produced - each daughter cell has a copy of the circular DNA, but a variable number of copies of the plasmid
40
What culture mediums can bacteria be grown in?
* a nutrient broth solution
* as colonies on an agar gel plate
* contains carbohydrates, minerals, proteins and vitamins needed to grow
41
How can bacteria be grown in a nutrient broth solution?
* Involves making a suspension of bacteria to be grown and mixing with sterile nutrient broth, stoppering the flask with cotton wool to prevent air from contaminating it and shaking regularly to provide oxygen for the growing bacteria
42
How can bacteria be grown on an agar gel plate?
* The agar acts as the culture medium and bacteria grown on it forms colonies on the surface
* To make the plate hot sterilised agar jelly is poured into a sterilised Petri dish, which is left to cool and set
* Inoculating loops are dipped in a solution of the microorganism and spread over the agar evenly
* A lid is taped on and the plate is incubated for a few days so the microorganisms can grow (stored upside down)
43
What are uncontaminated cultures of microorganisms required for?
* investigating the action of disinfectants and antibiotics
44
How do you calculate the number of bacteria in a population after a certain time if given the mean division time?
* 2 to the power of the amount of divisions
45
How do you sterilise Petri dishes and culture medium and why?
* using UV or an incubator
* to kill any unwanted microorganisms and prevent contamination
* could be harmless however, will will compete for nutrients and space
* or could be harmful (mutation) producing a new pathogen
46
How do you sterilise inoculating loops and why?
* pass it through a flame
* the flame kills any unwanted microorganisms and prevents contamination
47
What is the inoculating loop used for?
* transferring microorganisms to the media
48
Why must the lid of the Petri dish be secured with adhesive tape?
* to prevent the lid falling off and unwanted airborne microorganisms entering
49
Why must the Petri dish not be completely sealed?
* Sealing it would result in harmful anaerobic bacteria growing
50
Why must the Petri dish be stored upside down into an incubator?
* to prevent condensation and moisture dripping down onto the bacteria and disrupting colonies
51
Why must cultures generally be incubated at 25ºC in school labs?
* to reduce the chance of harmful bacteria growing
* if we incubated it at higher temperatures, more dangerous microorganisms could grow
52
What does the nucleus of a cell contain?
* chromosomes made of DNA molecules
* each chromosome carries a large number of gene
* different genes control the development of different characteristics
53
What do chromosomes come in?
* pairs of 23
54
What is the cell cycle?
* body cells in multicellular organisms dividing to produce new cells
55
What happens during stage one of the cell cycle?
* interphase
* the cell physically grows to increase the amount of sub-cellular structures (replicates - e.g. ribosomes, mitochondria)
* DNA duplicates to form two copies of each chromosome (X-shaped)
56
What happens during stage two of the cell cycle?
* mitosis
* chromosomes line up at the centre of the cell and the cell fibres pull them apart
* membranes form around each of the sets of chromosomes
* one set of chromosomes is pulled to each end of the cell and the nucleus divides
57
What happens during stage three of cell cycle?
* cytokinesis
* the cytoplasm and cell membrane divide to form two genetically identical daughter cells
58
Why is cell division by mitosis important?
* allows for growth and development of multicellular organisms
* mitosis allows multicellular organisms to grow or replace cells that have been damaged
* vital part of asexual reproduction - involves one organisms so to produce offspring it replicates its own cells
59
Define a stem cell
* an undifferentiated cell of an organism which is capable of differentiating into any type of body cell
60
What is the function of stem cells in embryos?
* form when an egg and sperm cell fuse to form a zygote
* cells have not differentiated
* the stem cells can be cloned and made to differentiate into most different types of human cells
61
What is the function of stem cells in adult bone marrow?
* adult stem cells can only differentiate into many types of blood cell
62
What is the function of stem cells in meristem tissue?
* found in root and shoot tips
* can differentiate into any type of plant cell throughout the life of the plant
* can be used to make clones
63
What is therapeutic cloning?
* an embryo is produced with the same genes as the patient
* reduces the likelihood of immune rejection because it is not a foreign antigen - therefore they may be used for medical treatment
* once in the body, the embryonic stem cells could then differentiate and replace body cells that stopped working
64
What are the risk of therapeutic cloning?
* stems cells may become contaminated with a virus which could be passed on to the patient
65
What are the benefits of stem cells?
* cure diseases
* used to replace faulty cells
* make insulin-producing cells for people with diabetes
* make nerve cells for people who are paralysed
66
What are the benefits of stem cells from meristems?
* used to produce clones of plants quickly and cheaply
* rare species can be cloned to protect them from extinction
* grow identical plants with desirable features - e.g. disease resistance can be cloned
67
What are the advantages and disadvantages of using embryonic stem cells?
* can treat a wide variety / lots of diseases / problems
* many available / plentiful
* painless
* using them is better than wasting them (unwanted embryos from fertility clinics)
however:
*(possible) harm / death to embryo
* (relatively) untested / unreliable / may not work
* ethical or religious objections - potential life
* embryo can’t be ‘asked’ / ’embryo rights’ idea
68
What are the advantages and disadvantages of using adult stem cells?
* no ethical issues (in collection) / permission given
*quick recovery
* (relatively) safe well tried / tested / know they work
however:
* they don't treat as many diseases
* painful procedure
* risk of immune rejection due to foreign object being inside body
* risk of transferring viral infections when transferring adult stem cells from donor to patient
69
How do substances move into and out of cells?
* across the cell membranes via diffusion
70
Define diffusion
* the spreading out 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
* down a concentration gradient
71
What are the factors of affecting the rate of diffusion?
* difference in concentrations
* temperature
* surface area of membrane
72
How does difference in concentration affect the rate of diffusion?
* the greater the difference in concentration, the faster the rate of diffusion
* more particles are randomly moving down the gradient
73
How does temperature affect the rate of diffusion?
* the higher the temp, the higher the rate of diffusion
* increasing temp - more KE in particles, move faster, more collisions, therefore diffuses more quickly
74
How does surface area affect the rate of diffusion?
* as surface area increases, the rate of diffusion also increases
* more space for particles to move through
75
How does oxygen move in and out of cells via diffusion?
* cells need oxygen for aerobic respiration carried out by mitochondria
* cells are surrounded by a high concentration of oxygen because it is transported in the bloodstream from the lungs to the cells
* this means that there is a high concentration of oxygen outside the cells and a low concentration of oxygen inside the cells
* so oxygen diffuses from outside to inside the cell
76
How does carbon dioxide move in and out of cells via diffusion?
* CO₂ is produced as a waste product of respiration
* therefore there is a high concentration of CO₂ inside the cell and a low concentration outside the cell
* so the carbon dioxide diffuses out of the cell and into the blood
77
How does urea moves in and out of cells via diffusion?
* urea is a waste product produced inside cells
* it diffuses out of the cells into the blood plasma
* is excreted by the kidneys
78
What is the relationship between the size of an organism and its SA:V ratio?
* the smaller an organism is, the larger the surface area to volume ratio
79
Why does a unicellular not need any complex transport systems?
* a single-celled organism has a relatively large SA:V ratio
* this means they can use diffusion to transport molecules into their body from the air
* low metabolic demands means diffusion across the surface of the organism is sufficient enough
80
Why do large multi-cellular organisms (humans and plants) need transport systems to exchange substances with their environment?
* small SA:V ratio
* not enough substances can diffuse from their outside to surface to supply their entire volume
* need some sort of exchange surface for efficient diffusion
81
Why do we have organ systems?
* small SA:V ratio
* cells in the centre of the organism are too far away from the surface to get enough oxygen and other substances needed for life
* hence we have organ systems like the respiratory system and the circulatory system which has a very large surface area to allow us to get all the oxygen we need around our body
82
Why do multicellular organisms have exchange surfaces in organ systems?
* to compensate for the low SA:V ratio
83
What is the function of the small intestines?
* absorb glucose into the blood
84
How is the small intestine adapted for exchanging substances with the environment?
* has villi - increases SA of the small intestine, increases the rate of diffusion of nutrients like glucose or amino acids
* villi have a rich blood supply of capillaries to remove nutrients quickly - maintains a steep concentration gradient to increase rate of diffusion
* villi have a thin layer of cells (one cell thick) - short diffusion path
* the small intestine is very long - gives substances a long time to diffuse, gives it a large SA
85
What is the function of the lungs?
* to transfer oxygen to the blood and remove waste CO₂
86
How are the lungs in mammals adapted for exchanging substances with the environment?
* are ventilated - helps maintain the steep concentration gradient (new air is constantly being replaced), increasing the rate of diffusion
* they have thin alveolar walls (one cell thick) - short diffusion path of gases
* moist walls - gases dissolve in the moisture, helps them to diffuse
* permeable walls - allows gases to diffuse through
* made up of tiny sacs called alveoli - large surface area for gas exchange to take place
* well supplied with blood due to lots of capillaries covering the alveoli, constantly maintaining a large diffusion gradient
87
What is the function of the gills in fish?
* gills are the gas exchange surface in fish
* water enters the fish through the mouth and passes out through the gills
* as this happens, oxygen diffuses from the water into the blood in the gills
* CO₂ diffuses from the blood into the water
88
How are the gills in fish adapted for exchanging substances with the environment?
* each gill is made up of lots of gill filaments - gives it a large SA for exchange of gases - increases the rate of diffusion
* gills covered in lamellae - increases SA
* lamellae have lots of blood capillaries -increases rate of diffusion by removing oxygen quickly, helps maintain a steep concentration gradient
* blood flows through lamellae in one direction and water flows in the other - maintains steep concentration gradient between water and blood
* thin layer of surface cells - short diffusion pathway
89
What is the function of the stomata?
* carbon dioxide diffuses in through it
* oxygen and water vapour diffuse out through the stomata
90
How are the leaves in plants adapted for exchanging substances with the environment?
* have stomata that allow lots of carbon dioxide in and oxygen to diffuse out – maintaining a steep concentration gradient
* the air spaces increase the area of the exchange surface because the walls of the palisade cells are the site of gas diffusion
* relatively thin - short diffusion pathway for CO₂ to diffuse across
* flat shape - increases the SA
91
Why are the surfaces and organ systems of multicellular organisms specialised for exchanging materials?
* to allow sufficient molecules to be transported into and out of cells for the organism's needs
92
What is the effectiveness of an exchange surface is increased by?
* large surface area - more particles can move through
* thin membrane - short diffusion path
* having an efficient blood supply (in animals) - creates a steep conc gradient
* being ventilated (in animals, for gaseous change)
93
Define osmosis
* osmosis is the movement of water molecules
* from a region of higher water concentration (dilute) to a region of lower water concentration (concentrated)
* through a partially permeable membrane
94
What is a dilute solution and concentrated solution?
* dilute solution has a high concentration of water (high water potential)
* concentrated solution has a low concentration of water (low water potential)
95
Describe osmosis in the cytoplasm
* cytoplasm contains salts and sugars
* if placed in a dilute solution, water will move in
96
Define isotonic
* the concentration of sugar in the external solution is the same as the internal
* no movement of water
97
Define hypertonic
* the concentration of sugar in external solution is higher (less water) than internal
* water moves out
98
Define hypotonic
* the concentration of sugar in external solution is lower (more water) than internal
* water moves in
99
Describe osmosis in animals
* if external solution is more dilute (high water potential), it will move into the animal cells - causes them to burst
* if external solution is more concentrated (low water potential) excess water will leave the cell - causes them to become shrivelled
100
Describe osmosis in plants
* if the external solution is more dilute, water will move into the cell & vacuole, causing it to swell - results in pressure called turgor (essential in keeping the plant rigid)
* if the external solution is more concentrated, water will move out of the cell - cell membrane will move away from the call wall (plasmolysis) and die
101
Define active transport
* the movement of substances from an area of low concentration to high concentration
* against a concentration gradient
* requires energy
102
How does active transport work in the roots of plants?
* it allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil
* important because plants require ions for healthy growth
* mineral ions are usually higher in conc in the cells meaning diffusion cannot take place
* requires energy from respiration to work
103
How does active transport work in the gut?
* allows sugar molecules to be absorbed from lower concentrations in the small intestine into the blood which has a higher sugar concentration
* allows us to maximise our sugar intake so that digestion is more efficient
* important as sugar molecules are used for cell respiration
104
What are the differences between active transport, osmosis and diffusion?
* diffusion - movement of particles (high to low, doesn't require energy (passive process)
* osmosis - movement of water (high to low), doesn't require energy (passive process)
* active transport - movement of particles (low to high against conc gradient), requires energy
