WBBSE Madhyamik Life Science (English Adaptation) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Reflex arc

The nerve pathway that produces an automatic response without conscious control: receptor, sensory neuron, spinal cord relay, motor neuron and effector. It shortens reaction time and protects the body from injury.

Auxin and phototropism

Auxin produced at the shoot tip shifts to the shaded side under one-sided light, stimulating extra elongation there. The shoot therefore bends toward the light source, improving photosynthesis.

Cerebellum function

The part of the hindbrain that coordinates voluntary muscle activity, maintains posture and balance, and smooths movements. Damage causes unsteady gait and poor coordination, not paralysis.

Insulin and glucagon

Antagonistic pancreatic hormones controlling blood glucose. Insulin from beta cells lowers glucose by promoting cell uptake and glycogen storage; glucagon from alpha cells raises it by releasing glucose from liver glycogen.

Mitosis outcome

One diploid parent cell divides once to produce two genetically identical diploid daughter cells. It supports growth, tissue repair and asexual reproduction while conserving chromosome number.

Meiosis outcome

One diploid cell undergoes two divisions to give four haploid cells that differ genetically, owing to crossing over and independent assortment. These become gametes in sexually reproducing organisms.

Crossing over

Exchange of segments between non-sister chromatids of homologous chromosomes at chiasmata during prophase I of meiosis. It creates new allele combinations and increases genetic variation.

Test cross

A cross of an individual showing a dominant trait with a homozygous recessive partner. If any recessive offspring appear, the tested individual was heterozygous; if none appear, it was homozygous dominant.

X-linked recessive inheritance

A pattern where the gene lies on the X chromosome, so males with one affected X are affected while females need two. Carrier mothers transmit the allele to half their sons.

Thalassaemia

An autosomal recessive disorder in which defective haemoglobin chains cause anaemia. Carriers are usually healthy, but two carriers have a one-in-four chance of an affected child.

Sickle cell anaemia

A recessive condition from a point mutation in the beta-globin gene, replacing glutamic acid with valine. Low oxygen makes red cells sickle-shaped, causing pain, anaemia and blocked capillaries.

Down syndrome cause

Trisomy 21, an extra copy of chromosome 21 resulting from non-disjunction during meiosis. It gives 47 chromosomes and causes intellectual disability and characteristic facial features.

Homologous organs

Structures with the same basic origin and body plan but different functions, such as the forelimbs of humans, whales and bats. They indicate common ancestry and are evidence of divergent evolution.

Natural selection

The process where heritable variations that improve survival and reproduction become more common over generations, because their bearers leave more offspring. It is the main mechanism of evolution.

Binomial nomenclature

The two-part scientific naming system: genus name capitalised, species name in lower case, both italicised or underlined. It gives every species one universally recognised name.

Xerophyte adaptations

Features of plants in dry habitats: thick cuticle, sunken stomata, reduced or spiny leaves, water-storing tissue, and deep or widely spread roots. They reduce water loss and increase uptake.

Ten per cent law

Only about ten per cent of the energy at one trophic level passes to the next, the rest being lost mainly as heat. This limits food chains to about four or five levels.

Nitrogen fixation

Conversion of atmospheric nitrogen into usable ammonia compounds by organisms such as Rhizobium in root nodules and Azotobacter in soil, or industrially. It makes nitrogen available for protein synthesis.

Biomagnification

The increase in concentration of non-degradable pollutants such as DDT or mercury at each successive trophic level. Top predators therefore accumulate the highest, often harmful, concentrations.

Ex-situ conservation

Protection of endangered species outside their natural habitat, using zoos, botanical gardens, seed banks and gene banks. It complements in-situ protection of habitats such as parks and reserves.

Photosynthesis equation

6CO2 + 12H2O gives C6H12O6 + 6O2 + 6H2O in the presence of chlorophyll and light. Light reactions in thylakoids release oxygen; the Calvin cycle in the stroma fixes carbon.

Bile function

A liver secretion stored in the gall bladder and released into the duodenum. It contains no enzymes but neutralises acidic chyme and emulsifies fats into droplets for lipase action.

Villi adaptations

Finger-like projections of the small intestine lining that increase absorptive surface area. Each has a thin epithelium, rich capillaries for sugars and amino acids, and a lacteal for fats.

Nitrogen deficiency symptoms

Insufficient nitrogen causes poor growth, stunted stems and yellowing of older leaves, because nitrogen is needed for proteins, chlorophyll and nucleic acids. It is a macronutrient.

Anaerobic respiration in muscle

When oxygen is insufficient, glucose is broken down to lactic acid, releasing only about two ATP per glucose. Accumulated lactic acid causes fatigue and cramps until it is oxidised.

Double circulation

Blood passes through the heart twice per cycle: the pulmonary circuit to the lungs and the systemic circuit to the body. This keeps oxygenated and deoxygenated blood separate and maintains pressure.

Transpiration pull

Evaporation of water from leaf stomata creates tension in the continuous xylem water column, drawing water upward from the roots. It also aids mineral transport and cools the leaf.

Nephron reabsorption

In the proximal tubule, glucose, amino acids, most water and useful salts are reabsorbed from the filtrate into blood. Failure to reabsorb glucose results in glucose appearing in urine.

Negative feedback

A control mechanism in which a change in a factor triggers a response that reverses the change, restoring the set point. It keeps body temperature, glucose and water balance stable.

Sliding filament theory

Muscle contraction occurs when myosin heads bind actin and pull the filaments past each other, shortening the sarcomere. It requires ATP, calcium ions and nerve-released acetylcholine.

Ball and socket joint

A joint where a rounded head fits into a cup-shaped cavity, allowing movement in all planes plus rotation. Examples are the shoulder and hip joints.

Iodine starch test

Adding dilute iodine solution to a sample turns it blue-black if starch is present and leaves it brown if not. In leaf experiments the leaf must first be boiled in alcohol to remove chlorophyll.