Cells Flashcards
What is the function of the cell-surface membrane?
The cell-surface membrane controls the movement of substances into and out of the cell.
It is a selectively permeable membrane, allowing only specific molecules to pass through via diffusion, osmosis, or active transport.
It also plays a key role in cell communication and recognition through surface proteins.
What is the role of the nucleus in eukaryotic cells?
The nucleus contains the cell’s genetic material in the form of chromosomes (protein-bound, linear DNA).
It is surrounded by a nuclear envelope with pores to regulate the entry and exit of materials.
The nucleus is responsible for controlling cell activities such as growth, metabolism, and reproduction.
It also houses the nucleolus, where ribosomal RNA (rRNA) is synthesized.
What is the function of mitochondria?
Mitochondria are the powerhouses of the cell, responsible for producing ATP through aerobic respiration.
They have a double membrane, with the inner membrane folded into cristae to increase surface area for respiration.
Mitochondria also play roles in cell death, calcium storage, and heat generation.
What is the role of chloroplasts in plant and algal cells?
Chloroplasts are the sites of photosynthesis in plant and algal cells.
They contain chlorophyll, a pigment that absorbs light energy to convert carbon dioxide and water into glucose and oxygen.
Chloroplasts have a double membrane, with thylakoids inside that form granum structures, where the light-dependent reactions of photosynthesis occur.
What is the cell wall and where is it found?
Provides structural support.
Made of cellulose in plants & algae, and chitin in fungi.
What is the function of the cell vacuole in plants?
Maintains cell turgor for structure.
Contains cell sap (water, enzymes, sugars, ions).
What are ribosomes, and where are they found?
Site of protein synthesis.
Found free-floating or attached to the rough endoplasmic reticulum (RER).
What is the function of the rough endoplasmic reticulum (RER)?
Processes & folds proteins made by ribosomes.
How does the smooth endoplasmic reticulum (SER) differ from the RER?
Synthesizes & processes lipids (no ribosomes).
What is the Golgi apparatus and its function?
Modifies & packages proteins and lipids.
Forms Golgi vesicles for transport.
What is the function of Golgi vesicles?
Transport proteins & lipids within or out of the cell.
What are lysosomes, and what do they do?
Membrane-bound organelles that contain hydrolytic enzymes.
Break down worn-out cell parts & pathogens.
How do eukaryotic cells become specialised?
Certain genes are expressed or silenced to produce specialised structures for function.
How are specialised cells organised?
Cells → form tissues (groups of similar cells).
Tissues → form organs (e.g., heart, leaf).
Organs → form organ systems (e.g., digestive system, vascular system).
How do prokaryotic cells differ from eukaryotic cells?
Prokaryotic cells:
✔ Smaller than eukaryotic cells.
✔ No membrane-bound organelles (e.g., mitochondria, Golgi).
✔ Smaller ribosomes (70S vs. 80S in eukaryotes).
✔ No nucleus → single circular DNA molecule free in cytoplasm (not associated with histones).
✔ Cell wall made of murein (a glycoprotein).
What extra structures might some prokaryotic cells have?
Plasmids → Small, circular DNA that carries extra genes (e.g., antibiotic resistance).
Capsule → Slime layer that protects against immune attack & dehydration.
Flagella → Tail-like structure for movement.
Why are viruses considered acellular and non-living?
Not made of cells.
✔ Cannot reproduce independently → must infect a host cell.
✔ No organelles, ribosomes, or metabolism.
What are the key structural components of a virus?
Genetic material → Either DNA or RNA.
✔ Capsid → Protein coat surrounding genetic material.
✔ Attachment proteins → Allow virus to bind to specific host cell receptor
How do viruses infect cells?
1️⃣ Attachment proteins bind to host cell receptors.
2️⃣ Genetic material is injected or taken up.
3️⃣ Host cell replicates viral particles using its own machinery.
What is the principle of an optical (light) microscope?
Uses light and glass lenses to magnify images of specimens.
What is the maximum magnification and resolution of an optical microscope?
Magnification: ~1500x, Resolution: ~200nm.
What are the limitations of optical microscopes?
Low resolution, can’t see small organelles (e.g., ribosomes), requires thin specimens.
How does a transmission electron microscope (TEM) work?
A beam of electrons passes through a thin specimen; denser areas absorb more electrons and appear darker.
What are the advantages of TEM?
High resolution (~0.1nm), can see internal cell structures.
What are the limitations of TEM?
Requires very thin, dead specimens, produces black-and-white images, artefacts may be present.
How does a scanning electron microscope (SEM) work?
A beam of electrons scans the surface, producing a 3D image.
What are the advantages of SEM?
Produces detailed 3D images of the surface, doesn’t require thin sections.
What are the limitations of SEM?
Lower resolution than TEM (~1-20nm), only shows surface structures, can only be used on dead specimens.
How do you measure the size of an object under an optical microscope?
Use an eyepiece graticule calibrated with a stage micrometer.
What is the formula for magnification?
Magnification= size of image/size of real object
Define magnification.
The number of times larger an image is compared to the actual object.
Define resolution.
The ability to distinguish between two objects that are close together.
Which microscope has the highest resolution?
Transmission electron microscope (TEM) (~0.1nm).
What is the purpose of cell fractionation?
To separate organelles by density for study.
What are the two main steps of cell fractionation?
Homogenisation and ultracentrifugation.
What happens during homogenisation?
Cells are broken open using a homogenizer, releasing organelles into solution.
Why is the solution kept ice-cold, isotonic, and buffered?
Cold: Prevents enzyme activity that could damage organelles.
Isotonic: Prevents osmosis, stopping organelles from shrinking or bursting.
Buffered: Maintains pH, preventing enzyme denaturation.
What happens during ultracentrifugation?
The solution is spun at increasing speeds to separate organelles by mass.
What is an artefact in microscopy?
A structure that appears in an image but is not actually part of the specimen (e.g., air bubbles, preparation errors).
What organelles are separated at different centrifuge speeds?
Low speed → Nucleus (largest organelle).
Medium speed → Mitochondria & chloroplasts.
High speed → Lysosomes, endoplasmic reticulum, ribosomes (smallest).
Why did early scientists struggle to distinguish artefacts from real organelles?
Limited technology and image clarity made it difficult to confirm what was a true cell structure.
How did scientists confirm whether a structure was real or an artefact?
By repeating experiments, improving sample preparation, and comparing images from different microscopes.
Do all cells in multicellular organisms retain the ability to divide?
No, only some eukaryotic cells retain the ability to divide.
What is the cell cycle?
A series of events in a eukaryotic cell leading to division and replication.
During which phase of the cell cycle does DNA replication occur?
Interphase
What is mitosis?
The process of cell division where a eukaryotic cell produces two genetically identical daughter cells.
Why is mitosis important?
It ensures growth, repair, and asexual reproduction by producing genetically identical cells.
What happens during interphase?
DNA is replicated.
Organelles are duplicated.
ATP production increases.
Chromosomes are not visible under a microscope.
What happens during prophase?
Chromosomes condense and become visible.
Centrioles move to opposite poles.
Spindle fibers begin to form.
Nuclear envelope breaks down.
What happens during metaphase?
Chromosomes line up at the equator of the cell.
Spindle fibers attach to centromeres.
What happens during anaphase?
Spindle fibers contract, pulling sister chromatids apart.
Chromatids move to opposite poles of the cell.
What happens during telophase?
Chromatids reach opposite poles and decondense into chromatin.
Nuclear envelope reforms.
Spindle fibers break down.
What is cytokinesis?
The division of the cytoplasm, producing two daughter cells.
How can you recognize interphase in a microscope image?
The nucleus is visible, but chromosomes are not condensed.
How can you recognize prophase?
Chromosomes start condensing, and the nuclear envelope breaks down.
How can you recognize metaphase?
Chromosomes line up at the equator, with spindle fibers attached.
How can you recognize anaphase?
Chromatids are being pulled apart to opposite poles.
How can you recognize telophase?
Two new nuclear envelopes form, and chromatids become chromatin.
Why is mitosis a controlled process?
To ensure normal growth and prevent uncontrolled cell division
What happens when mitosis is uncontrolled?
It leads to the formation of tumors and cancer.
How do cancer treatments target mitosis?
By slowing or stopping cell division, often by:
Preventing DNA replication (stopping interphase).
Disrupting spindle fiber formation (stopping metaphase).
What is binary fission?
A form of asexual reproduction in prokaryotic cells.
What are the main steps of binary fission?
Replication of circular DNA and plasmids.
Cell grows, DNA moves to opposite ends.
Cytoplasm divides, forming two daughter cells.
How do daughter cells in binary fission differ from each other?
They each receive one copy of circular DNA but may get different numbers of plasmids.
Why don’t viruses undergo cell division?
They are non-living and lack cellular structures needed for division.
How do viruses replicate?
They inject their nucleic acid into a host cell, which then produces new virus particles.
What is the basic structure of all cell membranes?
A phospholipid bilayer with embedded proteins, glycoproteins, glycolipids, and sometimes cholesterol.
What is the function of phospholipids in the membrane?
They form a bilayer, creating a hydrophobic barrier that controls what enters and leaves the cell.
What is the fluid-mosaic model?
A model describing the cell membrane as:
Fluid: Phospholipids move within the bilayer.
Mosaic: Proteins, glycoproteins, and glycolipids are scattered throughout the membrane.
What is the role of proteins in the cell membrane?
Channel proteins: Allow specific ions/molecules to pass through.
Carrier proteins: Transport substances via facilitated diffusion or active transport.
Receptor proteins: Bind to molecules like hormones for cell signalling.
What is the role of glycoproteins and glycolipids?
Cell recognition (immune response).
Cell signalling (hormone binding).
Stability of the membrane.
What is the function of cholesterol in the membrane?
Restricts movement of molecules, making the membrane less fluid.
Increases membrane stability (especially at high temperatures).
What is simple diffusion?
The passive movement of molecules from high to low concentration directly through the phospholipid bilayer.
What types of molecules can move by simple diffusion?
Small, non-polar molecules (e.g., oxygen, carbon dioxide).
What factors affect the rate of diffusion?
Concentration gradient (steeper = faster).
Membrane surface area (larger = faster).
Membrane thickness (thinner = faster).
What is facilitated diffusion?
The passive movement of molecules across a membrane via channel or carrier proteins.
What types of molecules require facilitated diffusion?
Large or charged molecules (e.g., glucose, ions).
How do channel proteins work?
They form pores in the membrane, allowing specific ions to pass through.
How do carrier proteins work?
They change shape to transport molecules across the membrane.
What factors affect the rate of facilitated diffusion?
Number of channel/carrier proteins (more = faster).
Concentration gradient (steeper = faster).
What is osmosis?
The diffusion of water from a region of higher water potential to lower water potential across a partially permeable membrane.
What is water potential (Ψ)?
The tendency of water to move; pure water has the highest water potential (Ψ = 0 kPa).
What happens to an animal cell in pure water?
Water enters by osmosis → Cell bursts (lysis).
What happens to a plant cell in pure water?
Water enters by osmosis → Becomes turgid, but the cell wall prevents bursting.
What happens to an animal cell in a concentrated solution?
Water leaves by osmosis → Cell shrinks (crenation).
What happens to a plant cell in a concentrated solution?
Water leaves by osmosis → Plasmolysis (cytoplasm pulls away from the cell wall).
Why is ATP needed for active transport?
ATP is hydrolyzed to provide energy for carrier proteins to change shape and transport substances.
What is active transport?
The movement of molecules against the concentration gradient (low to high) using carrier proteins and ATP.
How does active transport differ from facilitated diffusion?
Active transport requires ATP.
Moves against the concentration gradient.
Uses carrier proteins only (no channel proteins).
What is co-transport?
A type of active transport where one substance moves down its gradient, allowing another to move against its gradient.
How does the co-transport of sodium and glucose work in the ileum?
Sodium ions (Na⁺) are actively transported out of epithelial cells into the blood (lowers Na⁺ concentration inside).
Sodium moves back in from the ileum lumen via co-transport proteins, bringing glucose with it.
Glucose moves into the blood by facilitated diffusion.
How can cells increase the rate of transport across membranes?
Increase surface area (e.g., microvilli in the small intestine).
Increase number of channel/carrier proteins.
Maintain steep concentration gradients.
How does surface area affect diffusion?
A larger surface area increases the number of molecules that can diffuse at once, making transport faster.
How do transport proteins affect movement across membranes?
More channel/carrier proteins allow faster facilitated diffusion and active transport.
How do concentration or water potential gradients affect transport?
A steeper gradient results in faster diffusion/osmosis.
What is antigen variability?
When a pathogen changes its surface antigens due to genetic mutations or recombination.
How does antigen variability affect disease prevention?
Prevents long-term immunity as memory cells don’t recognize new antigens.
Reduces vaccine effectiveness (e.g., influenza virus mutates frequently).
Makes it harder for immune systems to mount a fast response.
What is phagocytosis?
The process by which phagocytes engulf and digest pathogens.
Describe the steps of phagocytosis.
Phagocyte recognizes foreign antigens.
Engulfs the pathogen, forming a phagosome.
Lysosomes release lysozymes into the phagosome.
Lysozymes digest the pathogen.
Phagocyte presents antigens on its surface (becoming an antigen-presenting cell).
What is the role of lysozymes?
They are enzymes that break down bacterial cell walls, destroying the pathogen.
What is the cellular response?
The activation of T lymphocytes in response to antigen-presenting cells.
What is an antigen-presenting cell (APC)?
A cell that displays antigens from a pathogen on its surface (e.g., phagocytes after engulfing pathogens).
What do helper T cells (TH cells) do?
Activate cytotoxic T cells (TC cells) to destroy infected cells.
Stimulate B cells to divide and produce antibodies.
Activate phagocytes to engulf pathogens.
What is the humoral response?
The activation of B lymphocytes to produce antibodies.
What is clonal selection?
B cell binds to antigen and is activated by a helper T cell.
B cell divides by mitosis into plasma cells and memory cells
What do plasma cells do?
They produce and secrete antibodies specific to the antigen.
What do memory cells do?
Remain in the body for faster secondary immune response.
Provide long-term immunity.
What is an antibody?
A protein produced by B cells that binds to specific antigens to form an antigen-antibody complex.
What is the structure of an antibody?
Two heavy chains & two light chains (Y-shaped).
Variable region (binds to specific antigens).
Constant region (same for all antibodies, binds to immune cells).
How do antibodies lead to antigen destruction?
Agglutination: Antibodies bind to multiple pathogens, clumping them together.
Phagocytosis: Phagocytes engulf and destroy agglutinated pathogens.
What is the primary immune response?
The first response to an infection, slow as B cells need to activate and produce plasma cells.
How do vaccines work?
They contain dead or weakened antigens that stimulate the immune system to produce memory cells.
What is the secondary immune response?
Faster and stronger because memory cells quickly produce antibodies.
Prevents symptoms from developing.
What is herd immunity?
When a large percentage of the population is immune, reducing the spread of disease and protecting unvaccinated individuals.
Why do vaccines sometimes fail?
Antigenic variation (e.g., flu virus mutates yearly).
Weakened immune response in some individuals.
What is active immunity?
When the body produces its own antibodies after exposure to an antigen.
What are the two types of active immunity?
Natural: From infection.
Artificial: From vaccination.
What is passive immunity?
Immunity gained without producing antibodies.
What are the two types of passive immunity?
Natural: Antibodies from mother to baby via placenta or breast milk.
Artificial: Injected antibodies (e.g., anti-venom).
How does active immunity differ from passive immunity?
Feature Active Immunity Passive Immunity
Antibody Production Yes (by the body) No (antibodies given)
Memory Cells Produced? Yes No
Long-Term Immunity? Yes No (antibodies break down)
Example Infection or vaccination Breast milk or antibody injection
What is the structure of the human immunodeficiency virus (HIV)?
Genetic material: Two strands of RNA.
Enzymes: Reverse transcriptase (converts RNA to DNA).
Capsid: Protein coat surrounding the RNA.
Lipid envelope: Surrounds the capsid, with embedded attachment proteins (gp120)
How does HIV infect helper T cells?
Attachment: HIV binds to receptors (CD4) on helper T cells.
Entry: Viral RNA and enzymes enter the T cell.
Reverse Transcription: Reverse transcriptase converts viral RNA into DNA.
Integration: Viral DNA is inserted into the host’s DNA.
Replication: The host cell produces new viral proteins and RNA.
Assembly & Release: New HIV particles bud off, destroying the T cell.
How does HIV cause the symptoms of AIDS?
HIV destroys helper T cells, weakening the immune system. This leads to:
Fewer helper T cells → B cells & cytotoxic T cells can’t be activated.
Weakened immune response → More infections (e.g., tuberculosis, pneumonia).
AIDS is diagnosed when the immune system is severely compromised.
Why do AIDS patients suffer from secondary infections?
The immune system cannot produce enough antibodies or activate phagocytes to fight infections.
Why don’t antibiotics work against viruses?
Antibiotics target bacterial cell walls, ribosomes, or enzymes, which viruses don’t have.
Viruses replicate inside host cells, so antibiotics can’t reach them without damaging human cells.
What are monoclonal antibodies?
Identical antibodies produced from a single type of B cell, specific to one antigen.
How are monoclonal antibodies used in targeted therapy?
Antibody is designed to bind to antigens on diseased cells (e.g., cancer cells).
A drug (e.g., chemotherapy or toxin) is attached to the antibody.
The antibody delivers the drug directly to the target cells, reducing damage to healthy cells.
How are monoclonal antibodies used in medical diagnosis?
Bind to specific antigens linked to diseases.
Can be used in pregnancy tests, cancer detection, or pathogen identification
What is the ELISA test?
A test that uses antibodies to detect specific antigens or antibodies in a sample.
How does the ELISA test work?
Antigen is fixed to a surface.
A specific antibody binds to the antigen.
A second antibody with an enzyme attaches to the first antibody.
Substrate is added → If antigen is present, the enzyme produces a color change.
What is ELISA used for?
Diagnosing infections (e.g., HIV, COVID-19) and detecting drugs or hormones.
What are some ethical concerns about vaccines?
Animal testing: Some vaccines are tested on animals before human trials.
Side effects: Some people may have adverse reactions.
Compulsory vaccination: Should vaccines be made mandatory to protect public health?
What are ethical concerns about monoclonal antibodies?
Animal use: Mice are often used to produce hybridoma cells.
Cost vs. accessibility: Expensive treatments may not be available to all patients.
