Topic 2 : Cells Flashcards
1
Q
What are the functions of the nucleus?
A
1 - Control centre through production of mRNA, tRNA and protein synthesis
2 - Retains genetic material in the cell
3 - Manufactures ribosomal RNA and chromosomes
2
Q
What is the structure of the nucleus?
A
Nuclear envelope - Double membrane, controls entry/exit of materials and contains reactions within the nucleus
Nuclear pores - Allows passage of large molecules
Nucleoplasm - Granular, jelly like material
Nucleolus - Manufactures ribosomal RNA and assembles ribosomes
3
Q
What are the functions of the mitochondrion?
A
1 - Site of aerobic respiration
2 - Produces ATP from respiratory substrates (glucose/proteins/lipids)
3 - Found in high numbers in metabolically active cells. Muscle cells and intestinal epithelial cells (active transport)
4
Q
What is the structure of the mitochondrion
A
Double membrane - Controls entry/exit of material. Inner membrane folds to form cristae
Cristae - Provides large surface area for the attachment of enzymes and other proteins involved in respiration
Matrix - Contains proteins, lipids, ribosomes and DNA. Allowing the mitochondria to make some of its own proteins. Enzymes involved in respiration are found here
5
Q
What is the structure of the chloroplast
A
Chloroplasts have a double membrane (chloroplast envelope) that is highly selective in controlling substance movement.
Inside, grana are stacks of thylakoids, which contain chlorophyll and other pigments for the light-dependent reaction (LDR) of photosynthesis.
Thylakoids have a large surface area for light absorption and electron transport.
The stroma is a fluid-filled matrix containing enzymes, ribosomes, and circular DNA, necessary for the light-independent reaction (LIR) (Calvin cycle).
6
Q
How are chloroplasts adapted for photosynthesis?
A
1 - Grana membranes provide a large surface area for attachment of chlorophyll
2 - Stroma fluid contains all the enzymes needed to make sugars
3 - Chloroplasts contain both DNA and ribosomes so they can synthesize proteins needed for photosynthesis
7
Q
Function of ribosomes
A
Site of protein synthesis
8
Q
Structure of ribosomes
A
Found in cytoplasm and RER
One large and one small subunit
80S in eukaryotic cells
70S found in prokaryotic cells, mitochondria and chloroplasts, is slightly smaller
9
Q
Function of cell wall
A
1 - Mechanical strength preventing bursting by osmotic pressure
2 - Allows water to pass along it and through the plant
10
Q
Structure of the cell wall
A
- Consists of a number of polysaccharides including cellulose
- Contains a thin layer, called the middle lamella, which marks the boundary between adjacent cell walls and cements adjacent cells together
- Contains pores between walls “plasmodesmata” allowing exchange and transport of substances between two cells
11
Q
What materials are plant, algae and fungal cell walls made from?
A
Plant - Cellulose (microfibrils)
Algae - Cellulose/glycoprotein
Fungal - Chitin
12
Q
What are the functions of the vacuole?
A
- Support plant cells by making them turgid
- Sugars/amino acids are temporary food store
- Pigments colour petals attracting pollinators
13
Q
What is the structure of the vacuole?
A
Fluid filled sac bound by a single membrane (tonoplast)
14
Q
Explain the adaptions of muscle cells
A
- More mitochondria due to high energy demands for muscle contractions
- More myofibrils for muscle contraction
15
Q
Explain the adaptions for sperm cells
A
- Flagellum so the cell can swim towards the egg
- More mitochondria for energy for movement
- Streamlined shape
16
Q
Explain the adaptions for phagocytes
A
- Increased lysosomes which are critical for the breakdown of pathogens and debris.
- Increased volumes of endoplasmic reticulum Involved in protein synthesis and processing
17
Q
Explain the adaptions for liver cells
A
- Smooth ER: Important for detoxification and lipid metabolism.
- Mitochondria: Due to high energy demands in the liver for detoxification processes.
- Golgi Apparatus: Involved in the modification and secretion of proteins.
18
Q
What is cell differentiation and what are its advantages
A
- Where un specialized or stem cells undergo specific changes in structure and function to become specialised with specific roles.
- Become efficient in performing specific functions so multicellular organisms can live
19
Q
How are tissues arranged into organs?
A
- Through aggregation.
- An organ is a combination of tissues that are coordinated to perform a specific function.
- e.g. heart and lungs
20
Q
How are cells arranged into tissues?
A
- A selection of similar cells are aggregated together to perform a specific function
- e.g. muscles, epithelium, connective tissue
21
Q
How are organs arranged to organ systems?
A
- Organs work together as a single unit known as an organ system. Grouped together to perform particular functions
- e.g. digestive system, respiratory system, circulatory system
22
Q
Explain how prokaryotic cells differ
A
- Smaller, no nucleus or nuclear envelope. Often also have a cell wall
23
Q
Explain the 8 organelles of a generalised bacterial cell
A
- Genetic material organised in a circular strand of DNA
- Cell wall, made of mucus
- Capsule, layer of slime protecting cell
- Ribosomes, smaller than in eukaryotic
- Cell surface membrane
- Plasmid, small circular section of DNA
- Flagellum, for locomotion
- Cytoplasm, jelly like, contains enzymes and other soluble materials
24
Q
Explain whether viruses are living or not
A
- Not living, contain nucleic acids (DNA/RNA) but can only multiply inside of a host cell
25
Describe the structure of virus particles and explain the role of each part
- Capsid, protein coat which encloses the nucleic acids
- Genetic material
- Reverse transcriptase enzyme
- Attachment protein, so the virus can identify and attach to a host cell
- Lipid envelope which encloses the whole virus apart from the attachment proteins
- Matrix, provides support and facilitates cellular interactions
26
Explain the difference between magnification and resolution
Magnification refers to the increase in apparent size, while resolution refers to the ability to distinguish between two separate points or details.
27
Before cell fractionation, the tissue is placed in what type of solution?
- Buffer solution, stop pH/denaturing enzymes
- Same water potential, stops water moving in via osmosis and causing them to burst
28
Describe the principles of cell fractionation and ultracentrifugation in separating cell components
- Tissue placed in buffer solution and the cell is fractionated. (blended or crushed) To disrupt tissues
- Sample then cooled to slow destructive enzymes breaking down cells
- Cell homogenate then placed in centrifuge, forcers separate the organelles. larger organelles experience greater force and move faster down the test tube. Start with relatively low spin.
- Nuclei form a pellet, remainder of the homogenate (supernatant) transferred to new test tube and span at a faster rate. New pellet formed contain mitochondria
- Repeat, and the new pellet will contain lysosomes, then again and the pellet will contain ribosomes
29
Describe how a light microscope works and explain the limitations
- Very thin (one cell thick) sample obtained, and stained with a dye
- Placed on a slide and held in place on a stage
- Light can pass through the one layer and the outlines of each cell and certain organelles will be seen through a microscope
- Objective lens near sample magnifies the image, presenting a large and real image
- focus and magnification adjustments refine image clarity and size for observation
- Limited resolution, limited by the wavelength of visible light.
- Magnification limits up to around 1000x
30
Explain how you would use an eyepiece graticule to measure cells
An eyepiece graticule, etched onto a microscope's eyepiece, is used to estimate the size of microscopic objects like cells. By calibrating it against a stage micrometre with known measurements, you can count the graticule divisions that a cell spans to calculate its size, providing approximate measurements for the cells being observed.
31
Explain how a transmission electron microscope works and its limitations.
Powerful beam of electrons to visualise ultra fine details of specimens. Some are deflected, some absorbed, or transmitted. Creating a detailed image.
- Sample must be extremely thin
- Must be in a vacuum environment to prevent air molecules scattering electrons
- Beam damage delicate materials or living samples
32
Explain how a scanning electron microscope works and its limitations
- A beam of electrons produced by an electron gun, scans over the sample and uses secondary electrons emitted to create the image. Creates a 3D image of surface morphology
- Samples for SEM must be dehydrated, dried, and coated with a conductive material (e.g., gold) to prevent charging and improve imaging. Preparing samples can alter their natural state and structure.
- Resolution not as good as TEMs.
33
What happens in mitosis
- Genetic material doubles, and the cell divides into 2 genetically identical daughter cells
34
Explain the role of spindle fibres
- Attach to the centromere of chromosomes, during anaphase they pull apart sister chromatids toward opposite poles of the cell
35
Why is mitosis important?
- Mitosis is fundamental for the continuity of life, allowing organisms to grow, repair damaged tissues, maintain homeostasis, and ensure the transmission of genetic information to new cells
36
Describe the behaviour of chromosomes during interphase, prophase, metaphase, anaphase and telophase of mitosis
Interphase - uncondensed genetic material in the form of uncoiled chromatin which is not visible as distinct, condensed chromosomes
Prophase - Chromatin condenses and forms visible chromosomes, nuclear envelope breaks down
Metaphase - Chromosomes align along the equator of the cell, spindle fibres attach to the centromere of each chromosome
Anaphase - Spindle fibres contract so the centromeres split, separating sister chromatids into individual chromosomes at opposite poles of the cell
Telophase - Chromosomes reach the poles and decondense back into chromatin. New nuclear envelopes begin to form around the separated chromosomes at each pole.
37
Describe the three stages of the cell cycle
Interphase - Cellular growth and normal metabolic activities, DNA replication takes place, further cell growth and preparation for cell division by cells synthesising proteins required for mitosis.
Mitosis - The division of the cell into 2 daughter cells.
Cytokinesis - Where a cells cytoplasm divides, resulting in 2 cells with complete set of genetic material and organelles
38
What can uncontrolled cell division lead to?
When cells divide uncontrollably, it can lead to the formation of tumors. Cancer occurs when these abnormal cells grow out of control, invade nearby tissues, and potentially spread to other parts of the body.
39
How do prokaryotic cells divide?
Binary fission, type of asexual reproduction. One parent cell divides into 2 daughter cells
40
How do viruses replicate?
- Attachment proteins binds to receptors on a host cell
- Virus or just nucleic acids enter host cell
- Reverse transcriptase converts viral RNA into viral DNA
- Following this, the host cell’s machinery is manipulated to produce viral proteins, allowing for the assembly of new viral particles within the host cell.
- Virus cell then buds off.
41
Describe and label the fluid-mosaic model of membrane structure
- Phospholipid bilayer (hydrophobic tail, hydrophilic head)
- Proteins embedded or attached to the bilayer, channel and carrier proteins used in co transport and facilitated diffusion
- Glycoproteins and glycolipids present
42
Why are phospholipids present in cell membranes?
- Barrier formation, hydrophilic and phobic heads and tails. Separates the internal cellular environment from the external surroundings.
- Selective permeability. Restricting passage of large or polar molecules
43
Why are glycoproteins and glycolipids present in cell membranes?
Unique tertiary structures help cells recognize each other and play roles in immune responses.
44
Explain the cell surface membranes permeability
Selective permeability. Size and charge, polar molecules and too large molecules cant diffuse through.
45
Why does simple diffusion happen?
Due to the tendency of molecules to move from higher concentration areas to area of lower concentration until equilibrium is reached
46
What is facilitated diffusion?
When molecules are too large, or polar and therefore cant pass via simple diffusion through the phospholipid bilayer, so they have to be transported via carrier or channel proteins creating specific pathways to aid the molecules passage from regions of higher to lower concentration
47
What affects the rate of diffusion?
- Steeper concentration, the faster the rate of diffusion.
- Higher temperatures increase kinetic energy of the molecule, causing them to move more rapidly. So higher diffusion rates
- Surface area , more contact between molecules and the medium. higher rate
- Molecular size, small molecules move faster and have higher rate of diffusion
48
Why does osmosis happen?
The driving force behind osmosis is the tendency of water molecules to move from regions of higher free water concentration (lower solute concentration) to regions of lower free water concentration (higher solute concentration). Until equilibrium is reached. This movement occurs because of the random motion of water molecules and their interaction with solute particles.
49
What is meant by solute, water potential and solution?
- Solute refers to the substance dissolved within a solvent, like salt in water.
-Water potential measures the tendency of water to move across a semi-permeable membrane, influenced by factors like solute concentration and pressure.
-A solution is a homogeneous mixture composed of a solvent (like water) and one or more solutes (substances dissolved within the solvent).
50
How does osmosis affect animal cells?
- In a hypotonic solution, water moves into cells via osmosis causing them to swell and burst.
- In a hypertonic solution, water moves out of the cell causing it to shrink or undergo dehydration.
- Therefore its important to maintain isotonic solutions where there's no net movement of water
51
How does osmosis affect plant cells?
- In a hypotonic solution, the vacuole fills with water and exerts pressure against the cell wall, providing structural support through the turgidity and allows the plant to stay rigid.
- In a hypertonic solution, water moves out of the cell, thus causing a loss of pressure and severe dehydration occurs, the cell membrane pulls away from the cell wall, resulting in wilting and cell damage/death.
52
How could cells be adapted for rapid transport across internal or external membranes?
- Increased transport proteins
- Increased surface area
53
Explain adaptations of specialised cells in relation to the rate of transport across their membranes (epithelial and red blood cells)
Epithelial Cells in the Small Intestine:
Microvilli: These finger-like projections vastly increase the surface area of the cell membrane. More surface area means more space for transport proteins, accelerating the absorption of nutrients like glucose and amino acids.
Abundance of Transport Proteins: Epithelial cells possess a high number of specific transport proteins on their membranes, such as glucose transporters, facilitating rapid uptake of nutrients.
Red Blood Cells (Erythrocytes):
Lack of Nucleus: Red blood cells lack a nucleus, maximizing space for haemoglobin, the oxygen-carrying protein. This adaptation ensures efficient oxygen transport across the cell membrane to and from tissues.
54
Explain co transport using the sodium potassium pump as an example.
- Sodium ions move into the cell through facilitated diffusion from the intestine into the epithelial cells.
- Glucose ions also enter the cell through co transport
- Active transport then moves the sodium ions from the epithelial cell region of low concentration to the blood capillary where there is a higher concentration. Via a sodium potassium pump, potassium enters the cell at this time.
- Glucose leaves the cell via facilitated diffusion into the blood capillary
55
What are the main defence mechanisms of the body?
- Physical barriers act as the first line of defence against pathogens
- Immune system defends body against pathogens that have entered the body and produce immunity
- Inflammatory response increases blood flow to isolate and eliminate pathogens and initiate an immune response
- Antigens and antibodies detect and destroy specific antigens
56
How does the body distinguish between its own cells and foreign material
- The tertiary structure of surface proteins
- Lymphocytes collide with cells in the foetus. Infection in the foetus is rare so all the cells are our own cells.
- Some lymphocytes will have receptors that fit exactly those of the own body cells, but these die or are supressed.
- The only remaining lymphocytes are those that might fit foreign material
57
Explain the process of phagocytosis.
Phagocyte attracted to the pathogen by chemical products of the pathogen, it will move towards it via a concentration gradient.
Receptors on the cell membrane of the phagocyte attach to chemicals on the surface of pathogen
Lysosomes within the phagocyte migrate towards the phagosome formed by engulfing the pathogen
The lysosomes release hydrolytic enzymes into the phagosome where they hydrolyse the pathogen
Hydrolysis products are absorbed by the phagocyte
58
What are examples of specific responses?
- Cell mediated responses (T lymphocytes)
- Humoral responses (B lymphocytes)
59
What are examples of non specific responses?
- Phagocytosis
- Physical barriers
60
What are the 2 different types of lymphocytes
- B-lymphocytes, mature in bone marrow, involve antibodies present in body fluids. Humoral responses
- T-lymphocytes mature in the thymus gland, then control cell mediated immunity (involving body cells)
61
What is the role of APC's in the cellular response?
To present antigens from pathogens, and move to lymph nodes where they present the antigens to T cells.
62
Explain the 4 steps of cell-mediated immunity
1- Phagocytosis occurs and macrophage becomes APC
2 - Specific T helper cells bind to the antigen
3- The activated Tc cell undergoes clonal expansion. This activates cytotoxic T cells to kill infected cells by making holes in their cell surface membranes
4 - Some activated Tc cells transform into memory T cells, provide long term immunity.
63
Describe the role of Th cells
Recognise antigens presented by APC's and activate other immune cells
64
Explain the steps of hormonal immunity
1 - Surface antigens of invading pathogen are taken up by a B cell
2 - The B cell processes the antigens and presents them on its surface
3 - Th cells attach to the processed antigens on the B cell, activating that B cell
4 - The B cell undergoes mitosis to give a clone of plasma cells
5 - Cloned plasma cells excrete the specific antibody which fits the antigen
6 - Some b cells develop into memory cells, providing long term immunity
65
What is an antibody?
Y-shaped proteins produced by B cells (specifically plasma cells) as a crucial part of the body's immune response.
66
Explain the formation of an antibody-antigen complex
Shape and chemical structure of the antigen fit precisely into the complementary binding site of the antibody
67
What are monoclonal antibodies? and how are they produced?
Laboratory-produced antibodies that are designed to specifically target and bind to a particular antigen.
68
What is passive immunity?
Passive immunity is the transfer of pre-formed antibodies or immune cells from one individual to another, providing immediate but temporary protection against a specific pathogen or toxin.
69
What is active immunity?
Active immunity is the body's immune response triggered by exposure to a pathogen or antigen, resulting in the production of antibodies or immune cells, providing long-term protection against future encounters with the same pathogen.
70
Why does vaccination rarely eliminate a disease?
Pathogen variations, and challenges in achieving herd immunity allows the disease to persist and circulate within populations.
71
Explain how HIV causes the symptoms of AIDS
HIV leads to the symptoms of AIDS by attacking and gradually destroying the immune system, specifically targeting T cells, so we are no longer able to become actively immune to infections
72
How are antibodies used in the ELISA tests?
Immobilised antibodies for a specific antigen concentrated in a specific area on the surface.
Once the sample is added, the antigens will bind to the antibody on the surface
Enzyme linked, mobile antibodies are added and will bind to the already bound antigens.
Substrate added will cause colour change in the enzyme. and appear as a positive result.
73
Why are antibiotics ineffective against viruses?
Antibiotics inhibit enzymes required for the production of a murein cell wall. So water enters cells by osmosis, causing them to burst.
Viral cells rely on host cells to carry out their metabolic activities. Antibiotics cannot reach viruses once they are in the host cells
74
Three results of the release of cytokines by Th cells during the immunological response
- Increase in activity of phagocytes
- Activation of B cells
- Maturation of B cells into plasma cells
- Formation of memory cells
