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B1 - BIOLOGY
CELL STRUCTURE AND TRANSPORT
| Question | Answer |
|---|---|
| What are the two types of cells? | Eukaryotic (plant and animal) Prokaryotic (bacteria) |
| What are the differences between eukaryotic and prokaryotic cells? | Prokaryotic cells are much smaller than eukaryotic cells. Eukaryotic cells contain membrane-bound organelles and a nucleus containing genetic material, while prokaryotes do not. |
| What is the prokaryotic cell wall composed of? | Peptidoglycan |
| How is genetic information stored in a prokaryotic cell? | Found free within the cytoplasm as : Chromosomal DNA (single large loop of circular DNA) Plasmid DNA |
| What are plasmids? | Small, circular loops of DNA found free in the cytoplasm and seperate from the main DNA. Carry genes that provide genetic advantages e.g. antibiotic resistance |
| What is order of magnitude? | A power to the base 10 used to quantify and compare size. |
| What is a centimetre (cm)? | 1x10⁻² metres |
| What is a millimetre (mm)? | 1x10⁻³ metres |
| What is a micrometre (μm)? | 1x10⁻⁶ metres |
| What is a nanometre? (nm)? | 1x10⁻⁹ metres |
| What is the difference in order of magnitude between a human hair (100 µm) and the HIV virus (length = 100 nm)? | 100 µm = 10-4 m 100 nm = 10-7 m -4-(-7) = -4 + 7 = 3 |
| List the components of both plant and animal cells | Nucleus Cytoplasm Cell membrane Mitochondria Ribosomes |
| List the additional cell components found in plant cells | Chloroplasts Permanent vacuole Cell wall |
| Other than storing genetic information, what is the function of the nucleus? | Controls cellular activities |
| Describe the structure of the cytoplasm | Fluid component of the cell. Contains organelles, enzymes and dissolved ions and nutrients. |
| What is the function of the cytoplasm? | Site of cellular reactions e.g. first stage of respiration. Transport medium. |
| What is the function of the cell membrane? | Controls the entry and exit of materials into and out of the cell. |
| What is the function of the mitochondria? | Site of later stages of aerobic respiration in which ATP (energy) is produced. |
| What is the function of the ribosomes? | Joins amino acids in a specific order during translation for the synthesis of proteins. |
| What is the plant cell wall made of? | Cellulose |
| What is the function of the plant cell wall? | Provides strength. Prevents the cell bursting when water enters by osmosis. |
| What does the permanent vacuole contain? | Cell sap (a solution of salts, sugars and organic acids). |
| What is the function of the permanent vacuole? | Supports the cell, maintaining its turgidity. |
| What is the function of chloroplasts? | Site of photosynthesis |
| Describe how sperm cells in animals are adapted to their function | Haploid nucleus contains genetic information. Tail enables movement. Mitochondria provide energy for tail movement. Acrosome contains enzymes that digest the egg cell membrane. |
| Describe how nerve cells in animals are adapted to their function | Long axon allows electrical impulses to be transmitted all over the body from the central nervous system. Dendrites from the cell body connect to and receive impulse. Myelin sheath insulates the axon speeds up the transmission of impulses. |
| Describe how muscle cells in animals are adapted to their function | Arrangement of protein filaments allows them to slide over each other to produce muscle contraction. Mitochondria to provide energy for muscle contraction. Merged cells in skeletal muscle allow muscle fibre contraction in unison |
| Describe how root hair cells in plants are adapted to their function | Large surface area to absorb nutrients and water from surrounding soil. Thin walls that do not restrict water absorption. |
| Describe how xylem cells in plants are adapted to their function | No upper or lower margins between cells to provide a continuous route for water to flow. Thick, woody side walls strengthen their structure and prevent collapse. |
| Describe how phloem cells in plants are adapted to their function | Sieve plates let dissolved amino acids and sugars be transported up and down the stem. Companion cells provide energy needed for active transport of substances along the phloem. |
| What is cell differentiation? | The process by which cells become specialised. |
| Why is cell differentiation important? | Allows production of different tissues and organs that perform various vital functions in the human body. |
| At what point in their life cycle do most animal cells differentiate? | Early in their life cycle |
| For how long do plant cells retain the ability to differentiate? | Throughout their entire life cycle |
| What is the purpose of cell division in mature animals? | Repair and replacement of cells |
| What changes does a cell go through as it differentiates? | Becomes specialised through acquisition of different sub-cellular structures to enable a specific function to be performed by the cell. |
| Define magnification | The number of times bigger an image appears compared to the size of the real object. |
| Define resolution | The smallest distance between two objects that can be distinguished. |
| How does a light microscope work? | Passes a beam of light through a specimen which travels through the eyepiece lens, allowing the specimen to be observed. |
| What are the advantages of light microscopes? | Inexpensive Easy to use Portable Observe both dead and living specimens |
| What is the disadvantage of light microscopes? | Limited resolution |
| How does an electron microscope work? | It uses a beam of electrons which are focused using magnets. The electrons hit a fluorescent screen which emits visible light, producing an image. |
| Name the two types of electron microscope | Transmission electron microscope (TEM) Scanning electron microscope (SEM) |
| What is the advantage of electron microscopes? | Greater magnification and resolution. |
| Why do electron microscopes have a greater magnification and resolution? | They use a beam of electrons which has a shorter wavelength than photons of light. |
| How have electron microscopes enabled scientists to develop their understanding of cells? | Allow small sub-cellular structures (e.g. mitochondria, ribosomes) to be observed in detail. Enable scientists to develop more accurate explanations about how cell structure relates to function. |
| What are the disadvantages of electron microscopes? | Expensive Large so less portable Require training to use Only dead specimens can be observed |
| How can magnification be calculated? | magnification = size of image / size of real object |
| What is standard form? | A way of expressing numbers - written as a figure between 1 and 10 multiplied by a positive or negative power of 10. |
| Write 0.005 in standard form | 5x10⁻³ |
| Write 10382 in standard form | 1.0382x10⁴ |
| How do bacteria multiply? | Binary fission (simple cell division) |
| How often do bacteria multiply? | Once every 20 minutes if enough nutrients are available and the temperature is suitable. |
| State 2 ways in which bacteria can be grown | Nutrient broth solution Colonies on an agar gel plate |
| What nutrients make up a nutrient broth solution? | All nutrients required for bacteria to grow including nitrogen for protein synthesis, carbohydrates for energy and other minerals. |
| What are uncontaminated cultures of microorganisms needed for? | Investigating disinfectant and antibiotic action. |
| Describe the preparation of an uncontaminated culture using aseptic technique | Use presterilised Petri dishes Pour sterile agar gel in Petri dish Sterilise inoculating loop Dip inoculating loop into solution & streak with loop on surface of the agar Put lid on Petri dish, secure it with tape, store upside down Incubate 25oC |
| Why must Petri dishes and culture media be sterilised before use? | To kill any bacteria already present. |
| Why must inoculating loops be sterilised by passing them through a Bunsen burner flame? | To kill any bacteria present on the inoculating loop. |
| Why must the Petri dish lid be secured with tape and the whole dish stored upside down? | Stops bacteria in the air contaminating the culture. The lid is not fully sealed to prevent the growth of anaerobic bacteria in a lack of oxygen. Upside down to prevent condensation from forming and dripping down onto the colonies. |
| Why are cultures incubated at 25oC in school laboratories? | Harmful pathogens are less likely to to grow at this temperature. |
| What is the formula used to calculate cross-sectional area of a bacterial colony or clear area around a bacterial colony? | πr2 = 3.14 r = radius (diameter/2) |
| How is the number of bacteria in a population after a certain time calculated from the mean division time? | Number of bacteria in population at end of time period = number of bacteria at the beginning of the time period x 2 number of divisions in the time period. Divide by mean division time. Express the answer in standard form if possible. |
| Calculate the number of bacteria that will be present after 3 hours for a population that divides every 15 mins and has 5 bacterium present now | 15 minutes = 0.25 hours 3/0.25 hours = 12 divisions 5 x 2¹² = 20480 or 2.048 x 10⁴ |
| What is diffusion? | The net movement of particles from an area of higher concentration to an area of lower concentration. |
| What three main factors affect the rate of diffusion? | Concentration gradient - larger gradient, faster diffusion. Temperature - higher temperature, faster diffusion. Surface area - larger surface area, faster diffusion. |
| Give examples of substances transported by diffusion in the lungs and the kidney | Lungs: oxygen diffuses into the blood from the lungs and carbon dioxide diffuses into the lungs from the blood, both down their concentration gradient. Kidney: urea diffuses from cells into blood plasma so it can be excreted in urine. |
| How are single-celled organisms adapted for diffusion? | They have a large surface area to volume ratio - maximises the rate of diffusion of molecules to meet the organism’s needs. |
| How is surface area to volume calculated? | Surface Area = Number of Sides x (Side Length x Side Width) Volume = Length x Width x Depth Ratio = Surface Area:Volume |
| What four factors increase the effectiveness of a gas exchange surface? | Large surface area Thin membrane (short diffusion path) Efficient blood supply (animals) Ventilation (animals) |
| What is osmosis? | The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane. |
| What is meant when a solution is isotonic to a cell? | The concentrations of the external and internal (inside cell) solutions are the same. |
| What is meant when a solution is hypertonic to a cell? | The concentration of the external solution is higher than that of the internal solution (inside cell). |
| What is meant when a solution is hypotonic to a cell? | The concentration of the external solution is lower than that of internal solution (inside cell). |
| What may happen when an animal cell is placed in a hypotonic solution? | Water moves into the cell, causing it to burst. |
| What may happen when an animal cell is placed in a very hypertonic solution? | Water moves out of the cell, causing it to shrivel up. |
| How do plant leaves and stems remain rigid? | Turgor pressure - water moves in by osmosis, causing the vacuole to swell and the cytoplasm to press against the cell wall. |
| What may happen when a plant cell is placed in a very hypertonic solution? | Water moves out of the cell by osmosis and the vacuole and cytoplasm decrease in size. The cell membrane may pull away from the cell wall, causing the cell to become plasmolysed. |
| What is active transport? | The movement of molecules from a more dilute solution to a more concentrated solution against a concentration gradient, using energy from respiration. |
| How do plant root hair cells use active transport? | Root hair cells use active transport to take up mineral ions from a more dilute solution in soils. Ions such as magnesium and nitrates are required for healthy growth. |
| How is active transport used to absorb the products of digestion? | Active transport is used to transport glucose from a lower concentration in the gut to a higher concentration in the blood. Glucose is then transported to the tissues where it can be used in respiration. |
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