Characteristics and classification of living organisms
State the seven characteristics of living organisms
Movement [1]
Respiration [1]
Sensitivity [1]
Growth [1]
Reproduction [1]
Excretion [1]
Nutrition [1] (Memory aid: MRS GREN)
State the organelle responsible for each of the following cellular processes:
Site of aerobic respiration [1 mark]
Site of protein synthesis [1 mark]
Contains genetic material (DNA) [1 mark]
Mitochondrion (plural: mitochondria) [1]
Ribosome [1]
Nucleus [1]
Define the term diffusion. [2 marks]
The net movement of particles from a region of higher concentration to a region of lower concentration [1], down a concentration gradient, as a result of their random movement [1].
State the chemical elements present in:
Carbohydrates [1 mark]
Proteins [1 mark]
Carbon, Hydrogen, Oxygen (C, H, O) [1]
Carbon, Hydrogen, Oxygen, Nitrogen (and small amounts of Sulfur) (C, H, O, N, S) [1]
Define the term enzyme. [2 marks]
State the substrate and product for the enzyme amylase. [2 marks]
A biological catalyst [1] that speeds up metabolic reactions without being consumed [1] (or a protein that functions as a biological catalyst).
Substrate: Starch [1]; Product: Maltose [1].
Organisms are classified using a binomial system.
Define the term binomial system. [1 mark]
The scientific name for the house cat is Felis catus. Identify the genus and the species. [2 marks]
A system of naming species that is internationally agreed, in which the scientific name is made up of two parts showing the genus and the species. [1]
Genus: Felis [1], Species: catus [1]
Name three structures found in a plant palisade mesophyll cell that are absent in a human liver cell. [3 marks]
Cell wall (made of cellulose) [1]
Chloroplasts [1]
Permanent central vacuole (containing cell sap) [1]
State what happens to a red blood cell and a plant cell when placed in pure (distilled) water.
Red blood cell: [1 mark]
Plant cell: [1 mark]
Red blood cell: Swells and bursts (lysis) [1].
Plant cell: Swells and becomes turgid (does not burst due to rigid cell wall) [1].
Match each biological macromolecule to its constituent basic unit (monomer):
Starch / Glycogen
Protein
Lipids (Fats and Oils)
Starch/Glycogen -> Glucose / Simple sugars [1]
Protein -> Amino acids [1]
Lipids -> Fatty acids and glycerol [1]
Describe how an enzyme works using the "lock and key" hypothesis. [3 marks]
The enzyme has an active site with a specific 3D shape [1].
The substrate molecule (key) has a complementary shape that fits into the active site (lock) [1].
They bind to form an enzyme-substrate complex, yielding products and leaving the enzyme unchanged [1].
Below are descriptions of four arthropods:
Arthropod A: 3 pairs of legs, 1 pair of antennae, wings present.
Arthropod B: 4 pairs of legs, no antennae.
Arthropod C: 5 pairs of legs, 2 pairs of antennae.
Arthropod D: More than 10 pairs of legs, 1 pair of antennae.
Identify the group of arthropods (Insects, Arachnids, Crustaceans, Myriapods) for each letter. [4 marks]
A: Insects [1]
B: Arachnids [1]
C: Crustaceans [1]
D: Myriapods [1]
An image of a plant cell measures 48 mm in length under a microscope. The actual length of the cell is 0.08 mm.
Calculate the magnification of the image. Show your working. [2 marks]
Formula: Magnification = image size / actual size = 48 mm / 0.08 mm [1]
Answer: x600 [1]
Explain how each of the following factors affects the rate of diffusion:
An increase in temperature [2 marks]
An increase in diffusion distance [1 mark]
Higher temperature increases the kinetic energy of particles [1], causing them to move faster and increasing the rate of diffusion [1].
Increasing diffusion distance decreases the rate of diffusion [1].
Describe how a student can test a food sample for:
The presence of starch [2 marks]
The presence of lipids using the ethanol emulsion test [2 marks]
Starch: Add iodine solution [1]. Positive color change: yellow-brown to blue-black [1].
Lipid: Dissolve sample in ethanol, pour the solution into water [1]. Positive result: cloudy white emulsion forms [1].
Explain why the rate of an enzyme-controlled reaction increases as the temperature rises from 10°C to 37°C (optimum temperature). [2 marks]
Molecules gain more kinetic energy and move faster [1].
Increases the frequency of successful collisions between active sites and substrates [1].
Ferns and flowering plants both belong to the plant kingdom.
State two features shared by ferns and flowering plants. [2 marks]
State one key difference in how ferns and flowering plants reproduce. [1 mark]
Any two from: Both have roots/stems/leaves; both contain vascular tissue (xylem/phloem); both contain chlorophyll/carry out photosynthesis. [2]
Ferns reproduce via spores, whereas flowering plants reproduce via seeds/flowers. [1]
Red blood cells and root hair cells are specialized cells.
Describe how the shape of a red blood cell is adapted to its function. [2 marks]
Describe how the root hair cell is adapted for the absorption of water and mineral ions. [2 marks]
Red blood cell: Biconcave disc shape increases surface-area-to-volume ratio for faster diffusion of oxygen [1]; lacks a nucleus to provide more space for hemoglobin [1].
Root hair cell: Long extension/projection creates a large surface area for absorption [1]; thin cell wall for a short diffusion distance / contains many mitochondria for active transport of ions [1].
Potato cylinders were placed in sucrose solutions of different concentrations (0.0 mol/dm3 to 1.0 mol/dm3). After 1 hour, the percentage change in mass was calculated.
At 0.0 mol/dm3, the potato gained mass. Explain why in terms of water potential. [2 marks]
At 0.8 mol/dm3, the potato lost mass and became soft. Name the state of the cells in this potato strip. [1 mark]
The water potential outside the potato was higher than inside the potato cells [1], so water moved into the potato cells by osmosis down a water potential gradient [1].
Plasmolyzed (or flaccid) [1].
DNA is a double-stranded molecule that carries genetic information.
Describe the shape/structure of a DNA molecule. [2 marks]
State the complementary base pairing rules for DNA. [2 marks]
Two strands twisted to form a double helix [1], joined together by cross-links between complementary bases [1].
Adenine (A) pairs with Thymine (T) [1]; Cytosine (C) pairs with Guanine (G) [1].
An enzyme works optimally at pH 2. When placed in a solution of pH 8, the reaction stops entirely.
Explain why the enzyme stops functioning at pH 8. [3 marks]
Extreme pH causes the enzyme to denature [1].
The bonds holding the protein structure break, changing the shape of the active site [1].
The substrate is no longer complementary to the active site, preventing enzyme-substrate complexes from forming [1].
Traditionally, organisms were classified based solely on morphology and anatomy. Modern classification relies heavily on DNA base sequences.
Explain why sequence analysis of DNA bases is more accurate than morphological analysis for determining evolutionary relationships. [2 marks]
Two species share a recent common ancestor. Describe what you would expect to find when comparing their DNA base sequences. [1 mark]
Morphology can be misleading due to convergent evolution (organisms evolving similar features independently) or adaptation to similar environments [1]. DNA base sequences reflect direct genetic inheritance / evolutionary ancestry [1].
Their DNA base sequences will be very similar / have a high percentage of identical base pairs [1].
Bacterial cells are prokaryotes, whereas plant and animal cells are eukaryotes.
State two structural features present in a bacterial cell that distinguish it from an animal cell. [2 marks]
State two structures present in plant cells that are absent in bacterial cells. [2 marks]
Bacterial cells have: murein/peptidoglycan cell wall, circular loop of DNA / plasmid, or lack a nucleus / membrane-bound organelles [2].
Plant cells have: nucleus, mitochondria, chloroplasts, or a cellulose cell wall [2].
Root hair cells take up nitrate ions from the soil against a concentration gradient.
Name the process used to absorb nitrate ions under these conditions. [1 mark]
Explain why this process requires oxygen and fails to occur if the soil becomes waterlogged (anaerobic). [3 marks]
Active transport [1].
Active transport requires energy / ATP [1]. Energy is released through aerobic respiration [1], which requires oxygen. Waterlogged soil lacks oxygen, halting aerobic respiration and stopping active transport [1].
A student tests a sample for sucrose (a non-reducing sugar) using Benedict's solution directly, but the result remains blue.
Describe the steps the student must take to yield a positive Benedict's test for this sample. [4 marks]
Add dilute hydrochloric acid (HCl) to a new sample and heat in a water bath (to hydrolyze sucrose into glucose and fructose) [1].
Neutralize the solution by adding sodium hydrogen carbonate / alkali [1].
Add Benedict's reagent and heat in a hot water bath [1].
Color changes from blue to green / yellow / brick-red precipitate [1].
A student investigates the effect of catalase enzyme concentration on the rate of oxygen gas production.
State two variables that must be kept constant during this experiment. [2 marks]
The student observes that beyond an enzyme concentration of 4%, the rate of reaction no longer increases and levels off. Explain why. [2 marks]
Any two: Temperature, pH, Substrate concentration, Volume of substrate solution [2].
Substrate concentration becomes the limiting factor [1]; all substrate molecules are already occupied / actively reacting, so adding more active sites has no additional effect [1].