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Biology Grade 12 - Unit 5: Human Biology
​1. The functional unit of the nervous system, responsible for transmitting electrical signals, is the:
A. Nephron
B. Neuron
C. Alveoli
D. Sarcomere
Answer: B
Explanation: Neurons are specialized cells that process and transmit information through electrical and chemical signals. A nephron is for the kidney, and alveoli are for the lungs.
​2. Which part of the brain is primarily responsible for coordinating voluntary muscle movements, posture, and balance?
A. Cerebrum
B. Medulla Oblongata
C. Cerebellum
D. Thalamus
Answer: C
Explanation: While the cerebrum initiates movement, the cerebellum (often called the "little brain") fine-tunes those movements to ensure they are smooth and balanced.
​3. In a "Reflex Arc," the signal usually travels to which structure before an action is taken, bypassing the conscious brain?
A. The Spinal Cord
B. The Pituitary Gland
C. The Frontal Lobe
D. The Liver
Answer: A
Explanation: Reflexes are emergency responses. To save time, the sensory impulse goes to the spinal cord and a motor impulse is sent back immediately. This is why you pull your hand from heat before you even "feel" the pain.
​4. Which division of the Autonomic Nervous System is responsible for the "Fight or Flight" response during stress?
A. Parasympathetic Nervous System
B. Sympathetic Nervous System
C. Somatic Nervous System
D. Central Nervous System
Answer: B
Explanation: The Sympathetic nervous system prepares the body for action by increasing heart rate, dilating pupils, and diverting blood to the muscles. The Parasympathetic system "rests and digests" after the stress is gone.
​5. Hormones are chemical messengers produced by endocrine glands. How do they travel to their target organs?
A. Through specialized nerve fibers
B. Through the lymphatic system only
C. Through the bloodstream
D. By diffusing through the skin
Answer: C
Explanation: Endocrine glands are ductless. They secrete hormones directly into the blood, which carries them throughout the entire body, though they only affect cells with the specific receptors for that hormone.
​6. Which gland is often called the "Master Gland" because it controls the functions of many other endocrine glands?
A. Thyroid Gland
B. Adrenal Gland
C. Pituitary Gland
D. Pancreas
Answer: C
Explanation: Located at the base of the brain, the Pituitary gland secretes hormones that trigger the thyroid, adrenal glands, and reproductive organs to release their own hormones.
​7. If a person's blood glucose level rises too high after a meal, which hormone is released by the pancreas to lower it?
A. Glucagon
B. Adrenaline
C. Insulin
D. Thyroxine
Answer: C
Explanation: Insulin acts like a "key" that allows glucose to enter cells for energy or be stored in the liver as glycogen, thereby lowering the sugar levels in the blood.
​8. What is the main function of the "Myelin Sheath" found around many axons?
A. To produce energy for the cell
B. To increase the speed of electrical impulse transmission
C. To manufacture neurotransmitters
D. To protect the cell from bacteria
Answer: B
Explanation: The myelin sheath acts as an electrical insulator. In myelinated neurons, the signal "jumps" between gaps (Nodes of Ranvier), making the transmission much faster than in unmyelinated fibers..
9. "Negative Feedback" is a mechanism used in homeostasis to:
A. Increase a change until a process is complete
B. Stop all biological processes
C. Reverse a change to return the system to its set point
D. Cause a disease state
Answer: C
Explanation: Most homeostatic controls (like temperature or blood sugar) use negative feedback. If something goes too high, the body works to bring it down; if it goes too low, the body works to bring it up.


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Biology Grade 11 - Unit 3: Enzymes

​1. Enzymes are classified as which type of biological macromolecule?
A. Polysaccharides
B. Globular Proteins
C. Triglycerides
D. Phospholipids
Answer: B
Explanation: Enzymes are specialized proteins with a complex 3D shape (globular). This shape is essential because it creates the specific "active site" where chemical reactions take place.
​2. The specific region on an enzyme where the substrate binds is known as the:
A. Allosteric site
B. Surface area
C. Active site
D. Inhibitor zone
Answer: C
Explanation: The active site has a unique shape and chemical environment that matches only one specific substrate. This is why enzymes are highly specific to the reactions they catalyze.
​3. What happens to an enzyme when it is "denatured" by high temperatures?
A. It works faster to keep up with the heat.
B. Its 3D shape changes, and the active site no longer fits the substrate.
C. It turns into a carbohydrate.
D. It disappears completely.
Answer: B
Explanation: Excessive heat breaks the weak hydrogen bonds holding the enzyme's shape together. Once the shape of the active site is lost, the enzyme is permanently "broken" and cannot function.
​4. According to the "Induced Fit" model, how does an enzyme interact with its substrate?
A. The active site is a rigid lock that never changes shape.
B. The substrate changes its shape to fit the enzyme.
C. The enzyme's active site shifts slightly to wrap more tightly around the substrate.
D. The enzyme and substrate only touch each other briefly.
Answer: C
Explanation: Unlike the older "Lock and Key" model, "Induced Fit" suggests the enzyme is flexible. When the substrate enters, the enzyme changes shape slightly to create a more perfect fit, like a glove molding to a hand.
​5. Most human enzymes have an "optimal temperature" of approximately:
A. 0°C
B. 37°C
C. 60°C
D. 100°C
Answer: B
Explanation: Human enzymes are evolved to work best at normal body temperature (37°C). If the temperature drops too low, the molecules move too slowly; if it goes too high, the enzymes denature.
6. A "Competitive Inhibitor" reduces enzyme activity by:
A. Binding to the active site and blocking the substrate.
B. Changing the pH of the solution.
C. Binding to a different part of the enzyme to change its shape.
D. Dissolving the enzyme's cell membrane.
Answer: A
Explanation: Competitive inhibitors have a similar shape to the substrate. They "compete" for the active site. If the inhibitor gets there first, the real substrate cannot bind.
7. "Non-competitive inhibitors" bind to a site other than the active site. This site is called the:
A. Primary site
B. Allosteric site
C. Secondary site
D. Catalyst site
Answer: B
Explanation: When a molecule binds to the allosteric site, it causes the whole enzyme to distort. This changes the shape of the active site so the substrate can no longer fit, even though the inhibitor isn't blocking the "door."
​8. How does an increase in substrate concentration affect the rate of an enzyme-controlled reaction?
A. The rate increases indefinitely.
B. The rate decreases immediately.
C. The rate increases until all active sites are saturated, then it levels off.
D. It has no effect on the rate.
Answer: C
Explanation: Initially, more substrate means more collisions with enzymes. However, once every available enzyme is busy (saturated), adding more substrate won't speed things up because the enzymes are already working at their maximum speed (Vmax).
​9. What is the role of a "Co-factor" or "Co-enzyme" (like vitamins or minerals)?
A. To block the enzyme's action.
B. To provide extra energy to the cell.
C. To assist the enzyme by helping the substrate bind to the active site.
D. To turn the enzyme into a hormone.
Answer: C
Explanation: Some enzymes are "incomplete" and require a non-protein helper (like Zinc, Iron, or Vitamin B) to become active. Without the co-factor, the enzyme cannot catalyze the reaction.

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Biology EUEE Mock Exam
Grade 11 and Grade 12👇

1. Which of the following is an example of "Learning from Nature" (Biomimicry) in technology?
A. Using a microscope to see bacteria.
B. Designing a high-speed train based on the beak of a kingfisher.
C. Burning fossil fuels for energy.
D. Using chemical fertilizers in farming.
Answer: B
Explanation: Biomimicry involves taking inspiration from biological designs to solve human engineering problems.

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Biology Grade 12 Unit 4 Evolution

1. Which of the following best defines biological evolution?
   A) Change in an individual's traits during its lifetime
   B) Change in the genetic composition of a population over generations
   C) The process by which organisms become perfectly adapted
   D) The spontaneous appearance of new species
   Answer: B
   Explanation: Evolution refers to changes in allele frequencies in a population across generations, not changes within an individual's lifetime.

2. Which theory of evolution proposes that acquired characteristics can be inherited?
   A) Darwin's theory of natural selection
   B) Lamarck's theory of inheritance of acquired characteristics
   C) Modern synthesis theory
   D) Punctuated equilibrium theory
   Answer: B
   Explanation: Lamarck proposed that traits developed or acquired during an organism's lifetime could be passed to offspring, a concept largely discredited today.

3. Which of the following is NOT considered evidence for evolution?
   A) Fossil record showing transitional forms
   B) Homologous structures in different species
   C) Similarities in embryonic development
   D) The presence of identical DNA sequences in all living organisms
   Answer: D
   Explanation: While all organisms share the same genetic code, identical DNA sequences across all life forms do not exist; variation in DNA supports evolutionary relationships.

4. Natural selection acts directly on:
   A) Genotypes
   B) Phenotypes
   C) Allele frequencies
   D) Mutations
   Answer: B
   Explanation: Natural selection acts on observable traits (phenotypes); the genetic basis (genotype) is selected indirectly based on phenotypic success.

5. When extreme phenotypes are favored over intermediate ones, this type of natural selection is called:
   A) Stabilizing selection
   B) Directional selection
   C) Disruptive selection
   D) Sexual selection
   Answer: C
   Explanation: Disruptive selection favors individuals at both extremes of a trait distribution, potentially leading to speciation.

6. Which hominid species is considered the earliest known member of the genus Homo?
   A) Australopithecus afarensis
   B) Homo habilis
   C) Homo erectus
   D) Homo sapiens
   Answer: B
   Explanation: Homo habilis, appearing around 2.4 million years ago, is widely regarded as the earliest species in the genus Homo, known for early stone tool use.

7. What role do mutations play in evolution?
   A) They always produce beneficial adaptations
   B) They are the ultimate source of new genetic variation
   C) They directly cause natural selection
   D) They eliminate harmful alleles from populations
   Answer: B
   Explanation: Mutations introduce new alleles into a population, providing the raw material upon which evolutionary forces like selection and drift act.

8. Genetic drift is most likely to have a significant effect in:
   A) Large, randomly mating populations
   B) Small, isolated populations
   C) Populations with high gene flow
   D) Populations under strong natural selection
   Answer: B
   Explanation: Genetic drift, random changes in allele frequencies, has greater impact in small populations where chance events can significantly alter genetic composition.

9. The movement of alleles between populations through migration is known as:
   A) Mutation
   B) Genetic drift
   C) Gene flow
   D) Natural selection
   Answer: C
   Explanation: Gene flow occurs when individuals immigrate or emigrate, transferring alleles between populations and reducing genetic differences.

10. Which renowned Ethiopian scientist is known for contributions to paleoanthropology and the discovery of early hominid fossils in the Afar region?
    A) Richard Leakey
    B) Berhane Asfaw
    C) Charles Darwin
    D) Louis Leakey
    Answer: B
    Explanation: Dr. Berhane Asfaw is a prominent Ethiopian paleoanthropologist who has contributed significantly to discoveries of early human ancestors in Ethiopia, including work on Australopithecus and early Homo species.

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