IGCSE/O Level Biology: Diet, Digestion, and Absorption

Comprehensive practice flashcards for students reviewing IGCSE/O Level Biology Topic 8 (Diet and Human Digestive System), focusing on key terms, nutrient functions, deficiency symptoms, and digestive anatomy.

Carbohydrates

A nutritional substrate primarily found in rice, bread, and potatoes that is used in aerobic respiration to release energy.

Lipids

Dietary elements found in butter and nuts used for long-term energy storage, thermal insulation, and cell membrane structure; they provide $37\,kJ/g$ of energy.

Proteins

Nutrients used for the growth and repair of tissues and the production of enzymes, antibodies, and hormones; they provide $17\,kJ/g$ of energy.

Vitamin C

A nutrient found in citrus fruits and broccoli required for the synthesis of collagen protein to maintain healthy skin, gums, and blood vessels.

Vitamin D

A nutrient obtained from oily fish, egg yolks, or sunlight that aids the chemical absorption of Calcium ions from the small intestine.

Calcium

A mineral essential for the mineralization and hardening of bones and teeth, as well as muscle contraction.

Iron

A core component of haemoglobin found in red meat and spinach used for binding and transporting $O_2$ in the blood.

Fibre

Indigestible bulk found in whole grains and fruit skins that facilitates peristalsis to prevent constipation.

Balanced Diet

A diet containing all essential nutrients required by the body in the correct proportions to maintain health and meeting daily metabolic energy demands.

Scurvy

A deficiency disease caused by a lack of Vitamin C, characterized by bleeding gums, loose teeth, and capillary fragility.

Rickets

A deficiency disease caused by a lack of Vitamin D or Calcium, resulting in bowed legs, bone pain, and soft bones.

Anaemia

A condition caused by a lack of Iron, leading to chronic fatigue, pale skin, and shortness of breath due to low haemoglobin.

Kwashiorkor

Severe protein deficiency with adequate calorie intake, characterized by an edematous (swollen) abdomen.

Marasmus

A form of malnutrition caused by reaching a severe deficiency of both protein and calories, resulting in extreme muscle wasting.

Iodine solution

A chemical reagent used to test for starch; it changes from orange-brown to blue-black if starch is present.

Benedict\u2019s solution

A blue reagent used to test for reducing sugars that, when heated in a water bath above $80^\circ C$, turns green, yellow, or brick-red.

Biuret reagent

A light blue solution used to test for protein that changes to purple, violet, or mauve in a positive result.

Ethanol Emulsion Test

A laboratory test for lipids involving dissolving a sample in ethanol and adding it to water to look for a milky-white, cloudy emulsion.

Physical Digestion

The process of breaking food into smaller pieces using mechanical force (teeth, stomach churning, or bile) without breaking chemical bonds.

Chemical Digestion

The breaking of covalent chemical bonds within large insoluble molecules to form small soluble ones, catalyzed by enzymes through hydrolysis.

Enamel

The extremely hard, acellular outer matrix of a tooth that protects it from physical abrasion.

Pulp Cavity

The central living zone of a tooth containing blood capillaries for nutrients and nerves for sensing pressure and pain.

Dental Caries

Tooth decay caused by bacteria in plaque respiring sugars anaerobically to produce acid, which dissolves enamel and dentine.

Amylase

A digestive enzyme that breaks down starch into maltose.

Lipase

An enzyme that breaks down lipids into fatty acids and glycerol.

Pepsin

A stomach protease that functions at an optimum acidic pH of $1.5$ to $2.0$.

Bile

A substance produced in the liver and stored in the gallbladder that emulsifies fats into small droplets to increase surface area.

Sodium Hydrogencarbonate

An alkaline substance found in bile and pancreatic juice that neutralizes acidic chyme in the duodenum to a pH of $8$.

Peristalsis

Waves of muscular contractions driven by the antagonistic coordination of circular and longitudinal smooth muscles to move food through the gut.

Achromic point

The point in a digestion investigation where iodine remains orange-brown, indicating all starch has been fully digested.

Absorption

The movement of digested food molecules and ions from the intestinal lumen across the epithelium into the blood or lacteals.

Assimilation

The uptake of absorbed nutrients from the blood into body cells for incorporation into cellular structures or use in metabolism.

Lacteal

The central lymphatic vessel within a villus responsible for absorbing fats (fatty acids and glycerol).

Microvilli

Tiny microscopic folds on the surface of individual epithelial cells in the small intestine that vastly increase surface area.

Hepatic Portal Vein

The unique blood vessel that transports newly absorbed nutrients, such as glucose and amino acids, directly from the ileum to the liver.

Deamination

The process in the liver where nitrogen-containing amino groups are removed from excess amino acids and converted into urea.

Atheromas

Fatty plaques formed by blood cholesterol that deposit within the walls of coronary arteries, potentially leading to heart disease.