Biology Questions for SSC CGL

Cell Structure and Function

The cell is the basic unit of life. SSC focuses on differences between plant and animal cells, and the function of key organelles. Prokaryotic cells (bacteria) lack a nucleus; eukaryotic cells (animals, plants, fungi) have a nucleus. Mitochondria is the powerhouse, chloroplasts are in plants only. Ribosomes make proteins. Endoplasmic reticulum and Golgi apparatus transport and package proteins.

• Plant cells have cell wall, large vacuole, chloroplasts; animal cells do not
• Nucleus contains DNA and controls cell activity
• Mitochondria produces ATP (energy) in both plant and animal cells
• Chloroplasts found only in plant cells — site of photosynthesis
• Ribosomes synthesize proteins; found free or attached to ER
• Lysosomes (animal cells only) act as cellular garbage disposal

Photosynthesis and Respiration

Photosynthesis is how plants make food using sunlight, water, and CO2. It occurs in chloroplasts and has two stages: light-dependent (thylakoid) and light-independent (stroma/Calvin cycle). Respiration is the reverse: cells break down glucose to release energy as ATP. Aerobic respiration uses oxygen; anaerobic respiration (fermentation) does not. SSC loves asking where these occur and the basic equation.

• Photosynthesis: 6CO2 + 6H2O + light energy → C6H12O6 + 6O2
• Light reactions occur in thylakoid membranes; produce ATP and NADPH
• Calvin cycle (dark reaction) occurs in stroma; produces glucose
• Aerobic respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (ATP)
• Glycolysis occurs in cytoplasm; Krebs cycle and ETC in mitochondria
• Anaerobic respiration produces lactic acid (muscles) or ethanol (yeast)

Human Digestive System

Digestion breaks down food into absorbable nutrients. The pathway is mouth → esophagus → stomach → small intestine → large intestine → rectum. Saliva (amylase), stomach acid (HCl), and pancreatic enzymes are key. Most absorption happens in the small intestine. SSC asks about enzyme locations, pH requirements, and function of organs.

• Mouth: saliva contains amylase (breaks starch); mechanical chewing begins
• Stomach: HCl and pepsin digest proteins; chyme (semi-liquid food) formed
• Small intestine: receives bile (emulsifies fat) and pancreatic enzymes; main absorption site
• Pancreas secretes digestive enzymes and bicarbonate to neutralize acid
• Liver produces bile; stores glucose as glycogen
• Large intestine: absorbs water and minerals; forms feces

Circulatory System

The heart pumps blood through arteries, capillaries, and veins. Oxygenated blood from lungs goes to the body; deoxygenated blood returns to the heart and lungs. Blood carries oxygen, nutrients, hormones, and waste. SSC tests heart chambers, blood vessel types, and blood composition.

• Heart has 4 chambers: 2 atria (receive blood), 2 ventricles (pump blood)
• Right side pumps deoxygenated blood to lungs; left side pumps oxygenated blood to body
• Arteries carry blood away from heart (thick-walled, high pressure)
• Veins carry blood to heart (thin-walled, low pressure, have valves)
• Capillaries allow exchange of oxygen, nutrients, and waste at tissue level
• Blood: plasma (55%) + RBC (oxygen), WBC (immunity), platelets (clotting)

Nervous System

The nervous system has two parts: central (brain and spinal cord) and peripheral (nerves). Neurons transmit signals via electrical and chemical means (neurotransmitters). Reflex arc is a quick response without brain involvement. Brain controls all body functions; spinal cord relays signals.

• Brain: cerebrum (thinking, memory), cerebellum (balance, coordination), medulla (breathing, heart rate)
• Spinal cord: relays signals between brain and body; controls reflexes
• Neurons: dendrite (receives), cell body (nucleus), axon (transmits)
• Synapse: gap between neurons; neurotransmitters cross the gap
• Reflex arc: stimulus → sensory neuron → spinal cord → motor neuron → response (no brain delay)
• Peripheral nervous system: somatic (voluntary) and autonomic (involuntary) nerves

Reproduction and Genetics

Sexual reproduction involves meiosis (produces gametes with half chromosomes) and fertilization. Asexual reproduction (mitosis) produces identical offspring. Genetics studies inheritance; Mendel's laws explain dominant and recessive traits. DNA is the genetic material; genes are segments of DNA.

• Mitosis: produces 2 identical diploid cells; occurs in somatic cells
• Meiosis: produces 4 non-identical haploid cells (gametes); occurs in reproductive organs
• Mendel's Law of Segregation: alleles separate during meiosis
• Mendel's Law of Independent Assortment: different traits assort independently
• Dominant trait masks recessive; homozygous has two same alleles, heterozygous has two different
• DNA structure: double helix with phosphate-sugar backbone and nitrogenous bases (A-T, G-C)

Ecology and Evolution

Ecology studies organisms and their environment. Food chains show energy flow; food webs show multiple chains. Ecosystems have biotic (living) and abiotic (non-living) factors. Evolution is change in species over time via natural selection. Adaptation is a trait that helps survival.

• Food chain: producer (plant) → primary consumer (herbivore) → secondary consumer (carnivore)
• Energy decreases at each trophic level (10% rule)
• Biotic: organisms; abiotic: temperature, light, water, soil
• Natural selection: organisms with beneficial traits survive and reproduce
• Adaptation: physical (thick fur) or behavioral (migration)
• Biodiversity: variety of species; high in tropical rainforests, low in deserts

• Confusing photosynthesis location: light reactions in thylakoid, Calvin cycle in stroma — not both in stroma
• Mixing up arteries and veins: remember Arteries Away (from heart), Veins back to heart
• Saying mitochondria is only in animal cells — plants have mitochondria too; only chloroplasts are plant-only
• Forgetting that meiosis produces 4 cells, not 2 — mitosis produces 2 identical cells
• Thinking all enzymes work at the same pH — pepsin works in acidic stomach, trypsin in alkaline small intestine

• ABCD for blood vessels: Arteries Away, Capillaries tiny, Veins back. Arteries thick, Veins thin.
• PER for respiration: Photosynthesis Eats CO2, Respiration Eats glucose
• Brain regions: Cerebrum = Conscious thinking, Cerebellum = Coordination, Medulla = Maintenance (breathing, heartbeat)
• Meiosis = Mating (produces gametes); Mitosis = Maintenance (produces body cells)
• NADPH and ATP are products of light reactions; glucose is product of dark reaction (Calvin cycle)

• SSC Tier-1 asks 5-7 biology questions in 60 seconds per question average — expect straightforward recall, not complex reasoning. Focus on definitions and locations.
• Photosynthesis and respiration equations appear almost every year — memorize both and know where each stage occurs.
• Human system questions (digestive, circulatory, nervous) are high-frequency — know organ functions and enzyme names.
• Genetics questions are usually simple Mendelian crosses or dominant/recessive trait identification — rarely complex pedigree analysis.
• Ecology questions test food chains and energy flow — the 10% rule (energy decreases per trophic level) is a favorite.
• Recent papers show increased focus on plant physiology (transpiration, photosynthesis) over animal anatomy — don't neglect plants.