unit 2 biology

• Mitosis is important in the life of an organism. State reasons why. [4] MS 1. Growth / increase in cell number; 2. Replace cells / repair tissue / organs / body; 3. Genetically identical cells; 4. Asexual reproduction / cloning;
• Explain why an electron microscope shows more detail of cell structure than a light microscope [2] electron microscope has a greater resolving power / objects closer together can be distinguishedelectron (beams) have a shorter wavelength;
• Explain the function of the golgi apparatus + vesicles Packages and mods proteins (e.g adding a carbohydrate to it)Vesicles transport proteins + lipids out of the cell to the CS membrane (using exocytosis)
• How are photomicrographs formed using a TEM? e- gun produces a beam of e- -> focused on specimen by electromagnet.beam passes through specimen, denser areas are absorbed causing dark spots.
• How are SEM images created? e- beam is directed from abovee- beams are scattered which are analysed by a computer to build a 3-D image.
• what are the functions of glycoproteins? [2] - act as recognition sites - help cells attach to one another + form tissues (e.g lymphocytes can recognise an organism's own cells)
• Discuss the advantages and disadvantages of using a transmission electron microscope. Advantages: Best magnification and resolutionAllows internal structures to be seen Disadvantages: Can't look at living cells → specimen need to be in a vacuumSpecimen must be very thinArtefacts presentLong preparation time and complex staining processDoesn't form a colour imageOnly 2D images produced
• What are lysosomes and their function? Membrane-bound vesicles found in the cytoplasm that contain a hydrolytic enzyme called lysozyme.They are responsible for digesting invading cells / breaking down work out components
• Recall the structure of chloroplasts [7] 1. Small, flattened structure found within plant and algae cells 2. Contains a double membrane 3. Stroma is an aqueous liquid found within these membranes (contains enzymes) 4. Contains structures within called thylakoids 5. Stacked thylakoids = grana 6. Grana linked to each other by thin, flat piece of membrane called a lamellae 7. Contains circular DNA and ribosomes
• What do prokaryotic cells have instead of Mitochondria? Mesosomes - these are in foldings of the cell membrane that provide a large surface area for the attachment of the enzymes involved in respiration.
• Explain why phospholipids form a bilayer in plasma membranes 1) Phospholipids have a polar phosphate group which are hydrophilic and will face the aqueous solutions 2) The fatty acid tails are non-polar and will move away from an aqueous envrionment 3) As both the intracellular fluid (cytoplasm) and extracellular fluid (tissue fluid) is aqueous, phospholipids form two layers with the hydrophobic tails facing inwards and the phosphate groups facing outwards, interacting with the aqueous environment.
• Outline the steps in preparing a ''temporary mount'' Start by pipetting a small drop of water onto the slide Use tweezers to place a thin section on top of the water dropAdd a drop of stain, e.g eosin to make cytoplasm show upUse a mounted needle to add a cover slip to protect the specimen. Try and avoid air bubbles.
• Describe the function of cholesterol in the cell membrane Cholestrol regulates the fluidity of the cell-surface membrane. Key Functions: - reduces lateral movement of other molecules including phospholipids - makes the membrane less fluid at high temperatures - prevent leakage of water and dissolved ions from the cell as it is hydrophobic
• The centre of the bilayer is hydrophobic so water-soluble substances can't easily pass through it.
• State the adaptations of the plasma membrane for its functions [6] 1. phospholipid bilayer forms a barrier (forms a barrier to water soluble substances) 2. fluid (can bend to take up differnet shapes, e.g to form vesicles / self repair) 3. channel proteins (let water soluble/charged particels substances through) 4. carrier proteins (allow for facilitated diffusion) 5. surface proteins (act as receptors) 6. cholesterol (regulates fluidity)
• Describe how substances move across cell surface membranes by facilitated diffusion MS [3] 1. Carrier / Channel Protein 2. Protein's are specific to substance 3. Substance moves down the concentration gradient
• Compare and contrast facilitated and simple diffusion Similarities: Passive Particles move down their concentration gradient Differences: Facilitated Diffusion uses transport proteins e.g carrier/channel
• Explain why the graph for facilitated diffusion levels off The curve levels off above a certain external concentration of substance as channel proteins are saturated with molecules.
• Contrast hypotonic vs hypertonic Hypotonic - a solution with more water and less solute Hypertonic - a soluton with less water and more solute
• What happens when you put an animal cell in pure water? swells and burst (water enters by osmosis)
• What happens when you put a plant cell in pure water? - swells but does not burst - cell wall prevents it from bursting - made of cellulose – strong material - the cell is Turgid (swollen)
• What happens when you put plant clels in concentrated sugar solution? - The cytoplasm and vacuole shrink and membrane pulls away from the cell wall - Becomes plasmolysed
• In some scenarios, more than one ion is transported using the same carrier protein. Describe an example fo this. SODIUM POTASSIUM PUMP 1. The sodium-potassium pump binds three sodium ions and a molecule of ATP (from inside the cell) 2. The splitting of ATP provides energy to change the shape of the channel. The sdoium ions are driven through the channel. 3. The sodium ions are released to the outside of the membrane, and the new shape of the channel allows two potassium ions to bind. 4. Release of the phosphate reverts the channel to its original form, releasing potassium ions on the inside of the membrane.
• Why would the loss of water kill bacterial/plant cells? Loss of water will stop metabolic reactions
• State the relationship between specialised cells and organ systems Specialised cells form tissues that perform specific functions. These form organs made of several tissue types, which form organ systems
• In what organelle are starch grains found and why? Chloroplasts - starch grains are a product of photosynthesis
• What are the cells called that line the ileum and contain microvilli? Epithelial Cells
• How is the concentration gradient of glucose (higher in the illeum, lower in the bloodstream) maintained? Blood is constantly being circulated by the heart, the glucose absorbed into the bloodstream is taken around the body and used in aerobic respiration. This helps to maintain the concentration gradient and maintain the rate of diffusion.
• Without mentioning co-transport, explain how the digestion of starch in the gut leads to an increase of glucose concentration in the blood. 1) Hydrolysed by enzymes, (amylase) 2) Produces glucose in the gut 3) Glucose is small enough to cross the gut wall into the blood
• Explain how epithelial cells absorb glucose via co-transport with sodium ions. MS [3] 1. Sodium ions actively transported from the ileum cell to blood 2. This maintains the concentration gradient for sodium to enter from gut, each coupled with a glucose molecule 3. Glucose enters by facilitated diffusion via a co-transport protein with sodium ions
• How would the addition of a respiratory inhibitor stop the absorption of amino acids in the ileum? MS [4] 1. No ATP produced 2. Sodium ions not moved out of the cell 3. No concentration gradient for sodium to move into the cell with amino acids, hence no amino acids are absorbed
• What is the collective term for microvilli? brush border
• Describe how bacteria divide. [4] Binary fissionReplication of circular DNADivision of cytoplasm to produce 2 daughter cellsEach with a single copy of circular DNA
• Explain how cells lining the ileum of mammals absorb glucose by co-transport with Na+ ions. [3] • Na+ actively transported from ileum cell to blood • Maintains diffusion grad for Na+ to enter cells from gut • Glucose enters by facilitated diffusion with Na+
• Describe the roles of centromeres. [3] Holds chromatids togetherAttaches chromatids to spindleAllows chromatids to move to opposite poles
• Give 4 reasons why mitosis is important in the life of an organism. [4] Growth in cell numberReplace cellsGenetically identical cellsAsexual reproduction
• 5.1 - What are the 2 types of responses involving lymphocytes? Cell mediated response, involving T lymphocytes Humoral response, involving B lymphocytes
• 5.1 - What 4 things do antigens allow the immune system to identify? pathogens non-self material toxins abnormal body cells
• 5.1 - A variety of molecules are present on a foreign cells surface. Why is it that the proteins are the most important? Highly specific tertiary structure Enormous variety Allows the immune system to distinguish one cell from another
• 5.1 - In what cases is an immune response disadvantageous? In organ transplants, immune system recognises these as non-self and attempts to destroy the transplant.