CSEC Human and Social Biology flashcards

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

Photosynthesis equation

Carbon dioxide plus water, in the presence of light and chlorophyll, produces glucose and oxygen. Light energy is converted to chemical energy stored in glucose.

Chloroplast structure

Organelle with stacked thylakoid membranes containing chlorophyll where light reactions occur, surrounded by stroma where the Calvin cycle fixes carbon dioxide into glucose.

Aerobic respiration equation

Glucose plus oxygen produces carbon dioxide, water and much energy. Most ATP is generated in the mitochondria via the Krebs cycle and electron transport chain.

Anaerobic respiration in humans

Glucose is broken down without oxygen into lactic acid with a small energy yield. Lactic acid builds up in muscles during vigorous exercise and is later removed.

Enzyme active site

The specific region of an enzyme where the substrate binds. Its shape is complementary to the substrate; high temperature or wrong pH changes the shape and denatures the enzyme.

Bile function

Bile is produced by the liver, stored in the gallbladder and released into the duodenum. It emulsifies fats into droplets and neutralises acidic food from the stomach.

Villi adaptation

Finger-like projections of the small intestine wall that increase surface area for absorption. Each contains blood capillaries and a lacteal for absorbing digested nutrients.

Assimilation versus egestion

Assimilation is the incorporation of absorbed nutrients into body cells and substances. Egestion is the removal of undigested food as faeces, not a metabolic waste process.

Xylem and phloem

Xylem transports water and mineral ions upward from roots to leaves. Phloem transports dissolved sucrose and amino acids bidirectionally between leaves, roots and growing regions.

Transpiration definition

Loss of water vapour from leaf surfaces, mainly through stomata. It creates the pull that draws water up the xylem and cools the plant.

Artery structure

Blood vessel carrying blood away from the heart. Thick muscular elastic walls withstand high pressure, and a narrow lumen maintains pressure and flow.

Double circulation

Blood passes through the heart twice per complete circuit. The right side serves the lungs and the left side serves the body, keeping oxygenated and deoxygenated blood separate.

Inhalation mechanism

The diaphragm contracts and flattens while intercostal muscles raise the ribs. Thoracic volume increases, pressure falls below atmospheric pressure and air enters the lungs.

Alveolus adaptations

Alveoli provide a large, thin, moist surface with a rich capillary supply. These features maintain a steep concentration gradient for rapid diffusion of oxygen and carbon dioxide.

Reflex arc pathway

Receptor detects a stimulus and sends an impulse along a sensory neurone to a relay neurone in the spinal cord, then a motor neurone to an effector.

Insulin and glucagon

Insulin lowers blood glucose by promoting uptake and glycogen storage. Glucagon raises blood glucose by converting glycogen to glucose. Both act by negative feedback.

Kidney nephron function

The glomerulus filters small molecules from blood. The tubule reabsorbs glucose, amino acids and water, while urea remains and is excreted as urine.

ADH action

Antidiuretic hormone increases water reabsorption from the collecting ducts into blood. More ADH produces smaller volumes of more concentrated urine.

Genotype and phenotype

Genotype is the combination of alleles an organism carries. Phenotype is the observable characteristic produced by the genotype interacting with the environment.

Dominant and recessive alleles

A dominant allele is expressed even when only one copy is present. A recessive allele is expressed only when two copies are present, one from each parent.

Monohybrid 3:1 ratio

Crossing two heterozygous parents for a single gene gives offspring phenotypes in a 3:1 ratio, dominant to recessive, with genotypes in a 1:2:1 ratio.

Test cross purpose

Crossing an organism showing a dominant trait with a homozygous recessive individual. Offspring ratios reveal whether the unknown parent is homozygous or heterozygous.

Complementary base pairing

In DNA, adenine pairs with thymine and guanine pairs with cytosine. In RNA, adenine pairs with uracil. Hydrogen bonds hold the paired bases together.

Transcription and translation

Transcription copies a DNA gene into messenger RNA in the nucleus. Translation at ribosomes uses transfer RNA to assemble amino acids in the coded order.

Sex determination in humans

Females have two X chromosomes and males have one X and one Y. The father's sperm determines the sex of the child.

Continuous variation

Characteristics such as height and body mass that show a range of values. They are controlled by many genes and influenced by environmental factors.

Cholera transmission

A bacterial disease spread by contaminated water and food. It causes severe watery diarrhoea and dehydration; chlorinated water and sanitation control its spread.

Malaria vector

Plasmodium parasites are transmitted by the bite of infected female Anopheles mosquitoes. Control uses mosquito nets, draining stagnant water and insecticides.

Antibody action

Antibodies are proteins produced by lymphocytes that bind specifically to antigens on pathogens, helping destroy them. Memory cells give a faster response on reinfection.

HIV and the immune system

HIV infects helper T-lymphocytes and destroys them, weakening immunity. AIDS is the stage when opportunistic infections, such as tuberculosis, become life-threatening.

Eutrophication sequence

Nitrate fertiliser washes into water, causing an algal bloom. Algae die and decompose, bacteria use up dissolved oxygen, and fish and other organisms die.

Greenhouse effect

Greenhouse gases such as carbon dioxide and methane trap outgoing infrared radiation, warming the atmosphere. Increased emissions raise global temperature and sea level.