National MDCAT Biology Flashcards

24 sample cards from the Biology deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Why are lysosomes called 'suicidal bags' of the cell?

   Because they contain hydrolytic (digestive) enzymes that can digest worn-out cell components and, on rupture, can digest the entire cell (autolysis).

2. What is the structure and function of a chromosome?

   A chromosome is a thread-like structure of DNA tightly coiled around histone proteins (forming chromatin); it carries genes and transmits hereditary information from one generation to the next.

3. What is a centromere, and how does it relate to chromosome classification?

   The centromere is the constricted region of a chromosome where the two sister chromatids are joined and to which spindle fibres attach. Its position (metacentric, submetacentric, acrocentric, or telocentric) classifies the chromosome shape.

4. How many chromosomes are present in a normal human somatic (body) cell, and how are they arranged?

   46 chromosomes arranged as 23 pairs: 22 pairs of autosomes and 1 pair of sex chromosomes (XX in females, XY in males).

5. What are receptors in a biological context?

   Receptors are specialized protein molecules or sensory structures that detect specific stimuli (chemical or physical signals) and initiate a response, such as cell-membrane receptors that bind hormones/neurotransmitters or sensory receptors that detect environmental changes.

6. Classify sensory receptors according to the type of stimulus they detect.

   Photoreceptors (light), chemoreceptors (chemicals/taste/smell), mechanoreceptors (touch/pressure/sound), thermoreceptors (temperature), and nociceptors (pain).

7. What is a neuron, and what are its three basic structural parts?

   A neuron is the structural and functional unit of the nervous system that transmits nerve impulses. Its three parts are the cell body (soma), dendrites (receive impulses), and the axon (carries impulses away).

8. Classify neurons by their function.

   Sensory (afferent) neurons carry impulses from receptors to the CNS; motor (efferent) neurons carry impulses from the CNS to effectors; interneurons (association neurons) connect neurons within the CNS.

9. What is a synapse, and how is a nerve impulse transmitted across it?

   A synapse is the junction between two neurons (or a neuron and an effector). The impulse is transmitted chemically when neurotransmitters are released from the presynaptic neuron, cross the synaptic cleft, and bind receptors on the postsynaptic membrane.

10. What is the myelin sheath, and what is its function?

    The myelin sheath is a fatty insulating layer (formed by Schwann cells) around the axon; it speeds up nerve impulse conduction via saltatory conduction (jumping between Nodes of Ranvier) and insulates the axon.

11. Name the three main parts of the human brain.

    The forebrain (cerebrum, thalamus, hypothalamus), the midbrain, and the hindbrain (cerebellum, pons, medulla oblongata).

12. What are the main functions of the cerebrum?

    The cerebrum controls higher functions: thinking, memory, intelligence, reasoning, voluntary movements, and interpretation of sensory information.

13. What is the function of the cerebellum?

    The cerebellum coordinates voluntary muscle movements, and maintains balance, posture, and body equilibrium.

14. State the functions of the medulla oblongata.

    The medulla oblongata controls vital involuntary functions such as heartbeat, breathing (respiration), blood pressure, and reflexes like coughing, sneezing, and swallowing.

15. What is the function of the hypothalamus?

    The hypothalamus regulates body temperature, hunger, thirst, sleep, and emotions, and links the nervous system to the endocrine system by controlling the pituitary gland.

16. What is an enzyme, and what is its chemical nature?

    An enzyme is a biological catalyst that speeds up biochemical reactions without being consumed. Chemically, most enzymes are globular proteins (some are RNA, called ribozymes).

17. List four key characteristics of enzymes.

    They are highly specific for their substrate, speed up reactions by lowering activation energy, are required in very small amounts, and remain unchanged at the end of the reaction (reusable).

18. Explain the 'lock and key' model of enzyme action.

    The model proposes that the enzyme's active site has a specific shape that fits only a particular substrate, like a key fitting a lock, ensuring enzyme specificity.

19. How do temperature and pH affect enzyme activity?

    Each enzyme has an optimum temperature and pH at which activity is maximum. Beyond these, activity declines and very high temperature or extreme pH denatures the enzyme, destroying its function.

20. Differentiate between a cofactor and a coenzyme.

    A cofactor is a non-protein helper required for enzyme activity; if it is an inorganic ion (e.g., Mg2+, Zn2+) it is simply a cofactor, while if it is an organic molecule (e.g., vitamins like NAD, FAD) it is called a coenzyme.

21. What is meant by enzyme specificity, and what determines it?

    Enzyme specificity means each enzyme acts only on a particular substrate or type of reaction; it is determined by the unique three-dimensional shape of the enzyme's active site.

22. What is activation energy, and how do enzymes affect it?

    Activation energy is the minimum energy required to start a chemical reaction. Enzymes lower the activation energy, allowing the reaction to proceed faster and at lower temperatures.

23. What is the fluid mosaic model of the cell membrane?

    It describes the plasma membrane as a fluid phospholipid bilayer in which proteins (integral and peripheral) are embedded like a mosaic, with the whole structure being dynamic and able to move laterally.

24. What are ribosomes made of, and what is their function?

    Ribosomes are made of ribosomal RNA (rRNA) and proteins; they are the sites of protein synthesis (translation) in the cell.

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