key concepts Flashcards
What is a eukaryotic cell?
Eukaryotic cells (animal and plant cells) have a nucleus and membrane-bound organelles.
What structures do all eukaryotic cells have?
Nucleus, cell membrane, mitochondria, and ribosomes.
What structures do plant cells have that animal cells do not?
Cell wall, chloroplasts, and a permanent vacuole.
What structures do prokaryotic cells have?
Chromosomal DNA, plasmid DNA, cell membrane, ribosomes, and flagella
What is a prokaryotic cell?
a cell without a nucleus, where DNA is free in the cytoplasm (e.g., bacterial cells).
What is the function of the nucleus?
Contains genetic material (DNA) that controls cell activities.
What is the function of the cell membrane?
Selectively permeable membrane that controls the movement of substances in and out of the cell.
What is the function of mitochondria?
Site of aerobic respiration, releasing energy.
What is the function of ribosomes?
Site of protein synthesis, where proteins are made.
What is the function of the cell wall?
strong structure made of cellulose that provides support and strength
What is the function of chloroplasts?
Contain chlorophyll, which absorbs light energy for photosynthesis.
What is the function of the permanent vacuole?
Contains cell sap,improves the cells rigidity
What is the function of chromosomal DNA?
Single circular strand of DNA that controls cell activities (no nucleus).
What is the function of plasmid DNA?
Small rings of DNA - code for extra genes to those provided by chromosomal DNA
What is the function of the cell membrane? (prokaryotic)
Controls what enters and leaves the cell.
What is the function of ribosomes in bacteria?
Site of protein synthesis, but smaller than eukaryotic ribosomes.
What is the function of flagella?
Long, thin whip-like’ tails attached to bacteria that allow them to move
How is the acrosome adapted for fertilisation?
Contains enzymes to digest the egg’s membrane, allowing fertilisation.
Why does a sperm cell have a haploid nucleus?
Carries half the genetic material (23 chromosomes) so it can combine with the egg’s DNA.
Why does a sperm cell contain many mitochondria?
Provides energy for movement to reach to the egg
Why does the cytoplasm contain nutrients?
Provides energy and raw materials for the developing embryo.
Why does an egg cell have a haploid nucleus?
Carries half the genetic material (23 chromosomes) to allow fertilisation.
How does the cell membrane change after fertilisation?
It hardens to prevent other sperm from entering, ensuring only one sperm fertilises the egg.
What is the function of the cilia?
Hair-like structures that sweep substances in one direction (e.g., move mucus out of the airways).
Where are ciliated epithelial cells found?
In the airways (trachea/bronchi) and fallopian tubes.
How has the light microscope contributed to our understanding of cell structure?
Light microscopes allow us to see cell structures such as the nucleus and cell membrane, but with limited resolution.
How has the electron microscope improved our understanding of cells
Electron microscopes have a higher resolution and allow us to see sub-cellular structures like ribosomes, mitochondria, and chloroplasts in greater detail.
Why is the resolution of a microscope important?
Resolution determines how clearly and sharply we can see structures. A higher resolution allows us to see smaller structures in more detail.
How have electron microscopes increased our understanding of sub-cellular structures?
They allow scientists to observe structures like the membrane systems within the mitochondria and the internal structures of ribosomes, leading to a deeper understanding of cell function.
Q: What are the key parts of a light microscope and their functions?
• Eyepiece lens – Used to view the specimen.
• Objective lens – Provides different levels of magnification.
• Stage – Holds the slide in place.
• Focus wheel – Adjusts to obtain a clear image.
• Turret – Rotates to change the objective lens.
What are the steps for using a light microscope?
- Place the slide on the stage and look through the eyepiece lens.
- Turn the focus wheel to obtain a clear image.
- Start with the lowest magnification objective lens.
- Increase magnification and refocus.
How do you prepare a biological specimen for a light microscope?
- Peel or collect a thin layer of cells using a cotton bud.
- Add a chemical stain to make cell structures visible.
- Place the sample onto a glass slide.
- Carefully lower the coverslip, avoiding air bubbles.
What are enzymes?
Biological catalysts that increase the rate of reactions without being used up.
What determines an enzyme’s function?
The shape of its active site, which is complementary to a specific substrate.
Describe the Lock and Key Hypothesis.
- The substrate binds to the enzyme’s active site, forming an enzyme-substrate complex.
- The reaction occurs, breaking or forming bonds.
- The products are released, and the enzyme remains unchanged.
What is enzyme specificity?
Enzymes only catalyse one reaction because their active site is complementary to only one substrate.
What happens when an enzyme is denatured
The active site changes shape, so the substrate can no longer bind, stopping the reaction.
How does temperature cause denaturation?
Too high: Bonds in the enzyme break, changing the active site.
• Substrate no longer fits, so the enzyme stops working.
How does pH cause denaturation?
• pH alters the forces that hold the enzyme’s amino acid chains together.
• This changes the shape of the active site, preventing substrate binding.
How does temperature affect enzyme activity?
Increases up to the optimum (≈37°C in humans) as molecules move faster and collide more.
• Above the optimum, enzymes denature, causing a rapid drop in activity.
How does pH affect enzyme activity?
Each enzyme has an optimum pH (usually 7, but stomach enzymes have a low pH).
• Too high or too low pH disrupts bonds, changing the active site → denaturation.
How does substrate concentration affect enzyme activity?
More substrate = faster reaction (more enzyme-substrate complexes form).
• Saturation point: After this, adding more substrate makes no difference because all active sites are occupied.
What enzyme is used in this experiment, and what does it do?
Amylase, which breaks down starch into maltose (a simple sugar).
How do we test for starch?
Use iodine solution:
• Blue-black = Starch present
• Orange = Starch broken down
What are the independent, dependent, and control variables?
Independent variable: pH (changed using buffer solutions)
• Dependent variable: Time taken for starch to break down
• Control variables: Temperature, enzyme & substrate concentrations, volume of solutions
Why is a Bunsen burner and water beaker used?
To keep the temperature constant during the reaction (control variable).
What are the key steps of the method?
- Place iodine drops in a spotting tile.
- Label a test tube with pH, place in water beaker, and heat for 3 minutes.
- Add 2 cm³ amylase, 2 cm³ starch, and 1 cm³ buffer solution to the test tube. Start a stopwatch.
- Every 10 seconds, use a pipette to add a drop of solution to iodine.
- Repeat until iodine stays orange (starch broken down). Record the time.
- Repeat for different pH buffers.
- Plot a graph: pH (x-axis) vs. time (y-axis).
What is the expected result?- enzyme practical
Fastest reaction at optimum pH (~7.0 for amylase).
• Slower reactions at pH too high or too low due to enzyme denaturation.
What is the formula for calculating the rate of enzyme activity?
Rate = Change / Time
In enzyme reactions, what does “change” refer to?
The amount of substrate broken down or product formed.
How would you convert the rate from g/min to g/hour?
Multiply by 60 (since 1 hour = 60 minutes).
Why do we use rate calculations in enzyme experiments?
To compare enzyme activity under different conditions, e.g. pH, temperature, substrate concentration.
What is the role of enzymes in biological reactions?
Enzymes are biological catalysts that speed up the synthesis and breakdown of carbohydrates, proteins, and lipids.
What do carbohydrases do?
Carbohydrases break down carbohydrates into simple sugars.
Give an example of a carbohydrase and its function.
Amylase breaks down starch into maltose.
Where is amylase produced?
Salivary glands, pancreas, and small intestine.
What do proteases do?
Proteases break down proteins into amino acids.
Give an example of a protease and its function.
Pepsin breaks down proteins into amino acids.
Where is pepsin produced?
Stomach (other proteases are produced in the pancreas and small intestine).
What do lipases do?
Lipases break down lipids (fats) into fatty acids and glycerol.
Where are lipases produced?
Pancreas and small intestine.
Why is the breakdown of carbohydrates, proteins, and lipids important?
The products (glucose, amino acids, fatty acids, and glycerol) are absorbed into the bloodstream and used to build new carbohydrates, proteins, and lipids or for respiration.
What type of enzymes are needed for synthesis of new biological molecules?
Different, more complex enzymes that increase the rate of reaction.
What is diffusion?
The net movement of particles from an area of high concentration to low concentration.
Does diffusion,osmosis and active transport require energy?
diffusion and osmosis do not require energy, it’s a passive process
active transport Yes, it requires energy from ATP produced from respiration.
Give two examples of substances transported by diffusion.
Oxygen (for respiration) and carbon dioxide (waste product).
What is osmosis?
The movement of water from a dilute solution to a more concentrated solution across a selectively permeable membrane.
What is active transport?
The movement of substances from a low concentration to a high concentration (against the concentration gradient), using energy from ATP.
Give an example of a process that uses active transport.
Absorption of mineral ions into root hair cells in plants.
What is the aim of the osmosis core practical?
To investigate the effect of sucrose solution concentration on the mass of potato disks due to osmosis.
Describe the method for investigating osmosis in potato disks.
- Cut potato into equal-sized disks (e.g., 2cm diameter).
- Blot disks with tissue paper to remove excess water.
- Measure and record the initial mass of each disk.
- Place the disks into sucrose solutions of different concentrations (e.g., 0%, 1%, 2%, etc.).
- Leave for a set time, then blot again to remove excess solution.
- Find difference in mass (end mass - start mass) and use the percentage change equation to calculate percentage gain or loss of mass.
What is the formula for calculating percentage change in mass?
(change in mass / start mass) x 100.
What does a positive percentage change indicate?
The potato has gained mass, meaning water entered by osmosis (placed in a dilute solution).
What does a negative percentage change indicate?
The potato has lost mass, meaning water left by osmosis (placed in a concentrated solution).
What is the independent variable?
The concentration of the sucrose solution.
What is the dependent variable?
The change in mass of the potato disks.
What are the control variables? (Give at least one example)
Size of potato disks (e.g., 2cm diameter), volume of sucrose solution, temperature, time in solution.
What happens when the potato is placed in distilled water?
Water moves into the potato cells by osmosis (from a dilute solution outside to a more concentrated solution inside), causing the potato to gain mass.
What happens when the potato is placed in a concentrated sucrose solution?
Water moves out of the potato cells by osmosis (from a dilute solution in the potato to a more concentrated solution), causing the potato to lose mass.
