[3.2] Cells Flashcards

Question

Describe the principles, advantages and disadvantages of scanning electron microscopes (SEM)

Answer 1

_PRINCIPLES_ - **Electrons** focused using **electromagnets**. - Electrons **deflected/bounce off** specimen surface which generates **3D** image of **surface**. _ADVANTAGES_ - **High** resolution due to **short wavelength** of electrons. - **High** magnification (x 1,000,000) - Specimen does not need to be thin. _DISADVANTAGES_ - **Can't** see internal structures. - Can only view **dead/dehydrated** specimens as uses a **vacuum**. - Complex **preparation** so **artefacts** often present. - Does **not** show colour.

Answer 2

- Scientists prepared specimens in **different ways**. - If an object was seen with **one technique but not another**, it was more likely to be an **artefact** than an organelle.

Answer 3

1. Note **formula and rearrange** if necessary. 2. Convert **units** if necessary - image and actual size must be in the **same** units. 3. **Calculate** answer and **check units** required or if **standard form** is required.

Answer 4

Metre (m) to centimetre (cm) = x100 **Centi**metre (cm) to millimetre (mm) = x10 **Milli**metre (mm) to micromere (µm) = x1000 **Micro**metre (µm) to nanometre (nm) = x1000 (To convert back, use the same numbers, but divide instead)

Answer 5

1. **Line up** scale of eyepiece graticule with scale of **stage micrometre**. 2. **Calibrate** eyepiece graticule by using **stage micrometre** to calculate **size of divisions** on **eyepiece graticule**. 3. Take micrometre away and use graticule to measure **how many divisions** make up the object. 4. Calculate the size of object by **multiplying** number of divisions by size of division. 5. **Recalibrate** eyepiece graticule at different magnifications.

Answer 6

1. **Homogenise** tissue/use a blender. - Disrupts **cell membrane, breaking open** cells and releasing contents/organelles. 2. Place in **cold, isotonic, buffered** solution. - Cold to **reduce enzyme activity** so organelles not broken down/damaged. - Isotonic so water doesn't move in or out of organelles by **osmosis** so they don't **burst**. - Buffered to keep **pH constant** so **enzymes** don't **denature**. 3. Filter homogenate - Remove large, unwanted cell **debris**. 4. **Ultracentrifugation** - separates organelles in order of **density/mass**. - Centrifuge homogenate in a tube at **high speed**. - Remove **pellet** of **heaviest** organelle and **respin supernatant** at a higher speed. - Repeat at increasing speeds until separated out, each time pellet made of lighter organelles (nuclei -> chloroplasts/mitochondria -> lysosomes -> ER -> ribosomes)

Answer 7

1. _INTERPHASE_ - S Phase - **DNA replicates** semi-conservatively leading to **2 chromatids (identical copies)** joined at a **centromere**. - G1/G2 - Number of **organelles** and volume of **cytoplasm** increase, protein synthesis. 2. _MITOSIS_ - **Nucleus divides** to produce 2 nuclei with **identical** copies of DNA produced by parent cell. 3. _CYTOKINESIS_ - **Cytoplasm** and **cell membrane** divide to form 2 new genetically identical daughter cells.

Answer 8

1. _PROPHASE_ - Chromosomes **condense**, becoming shorter/thicker, so **visible** and appearing as **2 sister chromatids** joined by a **centromere**. - Nuclear envelope breaks down. - **Centrioles** move to opposite poles forming **spindle network**. - Spindle fibres start to **attach** to chromosomes by their **centromeres**. 2. _METAPHASE_ - Spindle fibres **attach** to chromosomes by their **centromeres**. - Chromosomes align along **equator**. 3. _ANAPHASE_ - Spindle fibres **shorten/contract**. - Centromere divides pulling chromatids from each pair to opposite **poles** of the cell. 4. _TELOPHASE_ - Chromosomes **uncoil**, becoming **longer and thinner**. - Nuclear envelopes reform forming **2 nuclei**. - Spindle fibres/centrioles break down.

Answer 9

Within **multicellular organisms, not all cells** retain the ability to divide such as neurones. Only cells that do retain this ability go through a **cell cycle**.

Answer 10

Parent cell divides to produce 2 genetically identical daughter cells for: - **Growth** of multicellular organisms by increasing cell number. - **Replacing** cells to repair damaged tissues. - **Asexual** reproduction.

Answer 11

1. Mutations in DNA/genes **controlling mitosis** can lead to **uncontrolled cell division** (mitosis is a controlled process). 2. **Tumour** formed if this results in **mass of abnormal cells**. - **Malignant** tumour = **cancerous**, can **spread** (metastasis). - **Benign** tumour = **non-cancerous**, doesn't spread.

Answer 12

1. Some disrupt spindle fibre activity/formation. - So spindles do not attach to chromosomes by their **centromere** which means chromatids can't be **separated** to opposite poles (no **anaphase**) so prevents/slows **mitosis**. 2. Some prevent **DNA replication** during interphase. - So can't make 2 **copies** of each chromosome (**chromatids**) so prevents/slows **mitosis**. (Treatments more effective against cancer cells due to uncontrolled division, but disrupt cell cycle of rapidly dividing healthy cells too)

Answer 13

_BINARY FISSION_ 1. **Replication** of circular **DNA**. 2. **Replication** of **plasmids**. 3. **Division** of **cytoplasm** to produce 2 daughter cells that each contain a **single** copy of circular DNA and a **variable** number of copies of plasmids.

Answer 14

_Being **non-living**, viruses **do not undergo cell division**, instead:_ 1. **Attachment proteins** attach to complementary **receptors** on host cell. 2. Inject viral **nucleic acid** (DNA/RNA) into host cell. 3. Infected host cell replicates virus particles: - a. **Nucleic acid** replicated. - b. Cell produces viral **protein/capsid/enzymes**. - c. Virus **assembled** then **released**.

Answer 15

- Molecules free to **move laterally** in phospholipid bilayer. - Many components - **phospholipids, proteins**, glycoproteins and glycolipids. (The basic structure of all cell membranes, including cell-surface membranes and the membranes around the cell organelles of eukaryotes is the same)

Answer 16

1. **Phospholipids** - Form a **bilayer** - fatty acid tails face inwards, phosphate heads face outwards. 2. **Proteins** - **Intrinsic/integral** proteins span bilayer e.g. channel and carrier proteins. - **Extrinsic/peripheral** proteins on surface of membrane. 3. **Glycolipids** - Lipids with polysaccharide chains attached to them found on exterior surface. 4. **Glycoproteins** - Proteins with polysaccharide chains attached) found on exterior surface. 5. **Cholesterol** (sometimes present) - Bonds to phospholipid hydrophobic fatty acid tails.

Answer 17

- **Bilayer** with **water** present on either side. - **Hydrophobic** fatty acid tails **repelled** from water so point away from water/to interior. - **Hydrophilic** phosphate heads **attracted** to water so point to water.

Answer 18

**Restricts movement** of other molecules making up membrane so **decreases fluidity** and permeability/increases rigidity.

Answer 19

- Phospholipid bilayer is **fluid** so membrane can bend for **vesicle** formation/**phagocytosis**. - Glycoproteins/glycolipids act as **receptors/antigens** so involved in cell **signalling/recognition**.

Answer 20

- **Lipid-soluble (non-polar)** or very small substances (e.g. O₂, steroid hormones) move from an area of **high** concentration to an area of **low** concentration **down** a concentration gradient across **phospholipid bilayer**. - **Passive - doesn't** require energy from **ATP/respiration**, only **kinetic energy** of substances.

Answer 21

Restricts movement of **water-soluble (polar) and larger** substances (e.g. Na⁺, glucose) due to **hydrophobic fatty acid tails** in interior of bilayer.

Answer 22

- **Water-soluble / polar / charged**(or slightly larger substances) e.g. glucose & amino acids move from an area of **high** concentration to an area of **low** concentration **down** a **concentration gradient** through **specific channel/carrier proteins**. - **Passive - doesn't** require energy from **ATP/respiration**, only **kinetic energy** of substances.

Answer 23

- **Shape/charge** of protein determines which substances move. 1. **Channel** proteins facilitate diffusion of **water-soluble** substances. - **Hydrophilic pore** filled with water. - May be **gated** - can open/close. 2. **Carrier** proteins facilitate diffusion of slightly larger substances - **Complementary** substance attaches to **binding site**. - Protein changes **shape** to transport substance.

Answer 24

- **Water** diffuses from an area of **high water potential** to an area of **low water potential** down a water potential gradient through a **partially permeable membrane**. - **Passive - doesn't** require energy from **ATP/respiration**, only **kinetic energy** of substances.

Answer 25

- Water potential is a measure of how **likely** water molecules are to move out of a solution. - **Pure (distilled) water** has the **maximum** possible water potential (0 kPA). - **Increasing solute concentration decreases water potential**.

Answer 26

- Substances move from an area of **low** concentration to an area of **high** concentration against the concentration gradient. - Requires **hydrolysis** of **ATP** and specific **carrier proteins**.

Answer 27

1. **Complementary** substance **binds** to **specific carrier** protein. 2. **ATP** binds, hydrolysed into **ADP + Pi**, releasing energy. 3. Carrier protein **changes shape**, releasing substance on side of higher concentration. 4. Pi released - protein returns to **original shape**.

Answer 28

- **Two different** substances **bind** to and move **simultaneously** via a **co-transporter protein** (type of **carrier** protein). - Movement of one substance **against** its concentration gradient is often coupled with the movement of another **down** its concentration gradient.

Answer 29

_CO-TRANSPORT_ 1. **Na⁺ actively transported** from epithelial cells to blood by Na⁺/K⁺ pump establishing a **concentration gradient** of Na⁺ (higher in lumen than epithelial cell). 2. **Na⁺** enters epithelial cell **down** its concentration gradient with **glucose against** its concentration gradient via a **co-transporter protein**. 3. **Glucose** moves **down** a concentration gradient into blood via **facilitated diffusion**.

Answer 30

- Increasing surface area of membrane **increases** rate of movement. - Increasing number of channel/carrier proteins **increases** rate of **facilitated diffusion/active transport**. - Increasing concentration gradient **increases** rate of **simple/facilitated diffusion** and **osmosis**. - Increasing concentration gradient **increases** rate of **facilitated diffusion** until number of **channel/carrier proteins** becomes a **limiting factor** as **all in use/saturated**. - Increasing water potential gradient **increases** rate of **osmosis**.

Answer 31

1. Membranes **folded** (e.g. microvilli in ileum) increase **surface area**. 2. More **protein** channels/carriers for **facilitated diffusion** (or active transport - carrier proteins only) 3. **Large number** of **mitochondria** to make more **ATP** by aerobic respiration for **active transport**.

Answer 32

**Foreign molecule/protein**/glycoprotein/glycolipid that stimulates an **immune response** leading to production of an **antibody**.

Answer 33

- Each type of cell has **specific molecules** on its **surface** (cell-surface membrane/cell wall) that identify it. - Often they are **proteins** which have a **specific tertiary structure** (or glycoproteins/glycolipids).

Answer 34

1. **Pathogens** (disease-causing microorganisms) e.g. viruses, fungi, bacteria. 2. **Cells from other organisms** of the same species e.g. organ transplants. 3. **Abnormal body cells** e.g. tumour cells or virus-infected cells. 4. **Toxins** (poisons) released by some bacteria.

Answer 35

1. Phagocyte attracted by chemicals/recognises (foreign) antigens on pathogens. 2. Phagocyte **engulfs** pathogen by surrounding it with its cell membrane. 3. Pathogen contained in **vesicle/phagosome** in cytoplasm of phagocyte. 4. **Lysosome** fuses with phagosome producing a phagolysosome and releases **lysozyme** (hydrolytic **enzymes**). 5. Lysozymes **hydrolyse/digest** pathogen. 6. Phagocytosis leads to **presentation of antigens**, from the pathogen, where antigens are displayed on the phagocyte **cell-surface membrane**, stimulating the **specific** immune response (cellular and humoral response).

Answer 36

Specific **helper T cells with complementary receptors** on their cell surface bind to antigen on **antigen-presenting cells** (this could be infected cells, phagocytes, transplanted cells, tumour cells etc.) causing it to divide by mitosis to form clones which **stimulate**: 1. **Cytotoxic T cells** - kill infected cells/tumour cells (by producing perforin). 2. Specific **B cells** (humoral response). 3. **Phagocytes** - engulf pathogens by phagocytosis.

Answer 37

1. **Clonal selection:** - **Specific B lymphocyte** with **complementary receptor** (antibody on cell surface) binds to **antigen**. - This is then stimulated by **helper T cells** (which release cytokines). - So B lymphocyte divides rapidly by **mitosis** to form **clones**. 2. Some differentiate into **B plasma cells** and secrete large amounts of monoclonal **antibodies**. 3. Some differentiate into **B memory cells** and remain in blood for secondary immune response.

Answer 38

- **Quaternary structure proteins** (4 polypeptide chains). - Secreted by **B lymphocytes** e.g. plasma cells in response to **specific** antigens. - Bind **specifically** to antigens forming **antigen-antibody complexes**.

Answer 39

1. Antibodies **bind to antigens** on pathogens forming an **antigen-antibody complex**. - Specific **tertiary structure** so **binding site/variable region binds** to **complementary antigen**. 2. Each antibody binds to **2 pathogens** at a time causing **agglutination** of pathogens. 3. Antibodies **attract phagocytes**. 4. Phagocytes bind to the antibodies and **phagocytose many pathogens at once**.

Answer 40

_PRIMARY - FIRST EXPOSURE TO ANTIGEN_ - Antibodies produced **slowly** and at a **lower concentration**. - Takes time for specific **B plasma cells** to be stimulated to produce specific antibodies. - Memory cells produced. _SECONDARY - SECOND EXPOSURE TO ANTIGEN_ - Antibodies produced **faster** and at a **higher concentration**. - **B memory cells** rapidly undergo mitosis to produce many **plasma cells** which produce specific antibodies.

Answer 41

Injection of **antigens** from **attenuated** (dead or weakened) pathogens stimulating formation of **memory cells**.

Answer 42

1. Specific **B lymphocytes** with complementary receptor binds to **antigen**. 2. Specific **T helper cell** binds to **antigen-presenting cell** and **stimulates** B cell. 3. B lymphocyte divides by **mitosis** to form clones. 4. Some differentiate into **B plasma cells** and release **antibodies**. 5. Some differentiate into **B memory cells**. 6. On **secondary exposure** to antigen, **B memory cells** rapidly divide by mitosis to produce **B plasma cells**. 7. These release **antibodies faster** and at a **higher concentration**.

Answer 43

**Herd immunity - large proportion** of population vaccinated, reducing **spread** of pathogen. - Larger proportion of population **immune** so **do not become ill** from infection. - **Fewer infected** people to pass **pathogen** on/**unvaccinated** people **less likely** to come in **contact** with someone with disease.

Answer 44

_ACTIVE IMMUNITY_ - Initial exposure to **antigen** e.g. vaccine or primary infection. - **Memory cells** involved. - Antibody produced and secreted by **B plasma cells**. - **Slow**; takes **longer** to develop. - **Long-term** immunity as antibodies can be produced in response to a specific antigen **again** due to memory cells. _PASSIVE IMMUNITY_ - **No** exposure to antigen. - **No** memory cells involved. - Antibody introduced from **another organism** e.g. breast milk/across placenta from mother. - **Fast acting**. - **Short-term** immunity as antibody hydrolysed.

Answer 45

- Antigens on pathogens **change shape/tertiary structure** due to **gene mutations** creating new strains. - So **no longer immune** from vaccine or prior infection. - **B memory cell** receptors cannot bind to/recognise changed antigen on secondary exposure. - Specific antibodies **not complementary/cannot bind** to changed antigen. (**Examples:** yearly new flu vaccines, no vaccine for HIV, catch a cold many times)

Answer 46

1. **HIV attachment proteins** attach to **receptors** on **helper T cell**. 2. **Lipid envelope fuses** with cell-surface membrane, releasing **capsid** into cell. 3. Capsid uncoats, **releasing RNA** and **reverse transcriptase**. 4. **Reverse transcriptase** converts viral **RNA to DNA**. 5. Viral DNA **inserted/incorporated** into helper T cell **DNA**. 6. **Viral protein/capsid/enzymes** are produced - a. DNA **transcribed** into HIV mRNA. - b. HIV mRNA translated into new HIV proteins. 7. Virus particles are **assembled** and **released** from cell via budding or bursting the cell.

Answer 47

1. HIV infects and **kills helper T cells** as it multiplies rapidly. - So T helper cells can't stimulate **cytotoxic T cells, B cells** and **phagocytes**. - So plasma cells can't release as many **antibodies** for agglutination and destruction of pathogens. 2. **Immune system deteriorates** so more susceptible to infections. 3. Pathogens reproduce, release toxins and damage cells.

Answer 48

_Viruses do not have structures/processes that antibiotics inhibit:_ - Viruses do not have **metabolic processes/ribosomes**. - Viruses do not have **bacterial enzymes/murein cell wall**.

Answer 49

Antibodies produced from **genetically identical/cloned B lymphocyte/plasma cells** so have **same tertiary structure**.

Answer 50

1. Monoclonal antibody has **specific tertiary structure/binding site/variable region**. 2. **Complementary** to **receptor/protein/antigen** found only on a **specific cell type** (e.g. cancer cell). 3. **Therapeutic drug** attached to antibody. 4. Antibody **binds** to specific cell, forming **antigen-antibody complex**, delivering drug. (Some monoclonal antibodies are designed to **block antigens/receptors** on cells too)

Answer 51

1. Monoclonal antibody has a **specific tertiary structure/binding site/variable region**. 2. **Complementary** to specific **receptor/protein/antigen** associated with diagnosis. 3. **Dye/stain/fluorescent marker** attached to antibody. 4. Antibody **binds** to receptor/protein/antigen, forming **antigen-antibody complex**.

Answer 52

_DIRECT ELISA_ 1. Attach **sample** with **potential antigens** to well. 2. Add **complementary monoclonal antibodies** with **enzymes** attached which **bind** to antigens if present. 3. **Wash** well to **remove unbound antibodies** to prevent false positive. 4. Add **substrate** - enzymes create products that cause a **colour change** which indicates positive result. _SANDWICH ELISA_ 1. Attach **specific monoclonal antibodies** to well. 2. Add **sample** with **potential antigens**, then wash well. 3. Add **complementary monoclonal antibodies** with **enzymes** attached which **bind** to antigens if present. 4. **Wash** well to **remove unbound antibodies** to prevent false positive. 5. Add **substrate** - enzymes create products that cause a **colour change** which indicates positive result.

Answer 53

_INDIRECT ELISA_ 1. Attach **specific antigens** to well. 2. Add **sample** with **potential antibodies**, wash well. 3. Add **complementary monoclonal antibodies** with **enzymes** attached which **bind** to antibodies if present. 4. **Wash** well to **remove unbound antibodies** to prevent false positive. 5. Add **substrate** - enzymes create products that cause a **colour change** which indicates a positive result.

Answer 54

- Compare to test to show only **enzyme** causes colour change. - Compare to test to show all unbound antibodies have been **washed away**.

Answer 55

1. Pre-clinical testing on/use of **animals** - potential **stress/harm/mistreatment**. - But animals **not killed** and help produce new drugs to reduce **human suffering**. 2. Clinical trials on **humans** - potential **harm/side-effects**. 3. Vaccines - may still **develop/pass on pathogen**. 4. Use of drug - potentially dangerous **side effects**.

Answer 56

- Was the **sample size** large enough to be representative? - Were participants **diverse** in terms of age, sex, ethnicity and health status? - Were **placebo/control groups** used for comparison? - Was the **duration** of the study long enough to show long-term effects? - Was the trial **double-blind** (neither doctor/patient knew who was given drug or placebo) to reduce bias?

Answer 57

- What **side effects** were observed and how frequently did they occur? - Was a **statistical test** used to see if there was a significant difference start and final results? - Was the **standard deviation** of final results large, showing some people did not benefit? - Did **standard deviations** of start and final results **overlap**, showing there may not be a significant difference? - What **dosage** was optimum? Does increasing dose increase effectiveness enough to justify extra cost? - Was the **cost of production and distribution** low enough?

Answer 58

- Antibody with **enzyme remains** / not washed out. - So **substrated converted** into **colour** product.

[3.2] Cells Flashcards

Cell Structure, All Cells Arise from other Cells, Transport Across Cell Membranes, Cell Recognition & the Immune System (84 cards)