organisms exchange substances with their environment

• The bigger the cube (organism) the surface area to volume ratio decreases
• single cellular organisms exchange materials by diffusion with their environment and they need a short diffusion path which limits the size of the organism(<1mm)
• SIngle cellular organism have a large SA:V ratio which gives a short diffusion pathway
• multi cellular organism are larger than 1mm and each human contains about 10x14 cells
• larger organisms have all evolved adaptations with a large surface area and most have special exchange systems
• Breathing pathway: atmospheric air, nasal chamber or mouth, trachea, bronchi,bronchioles,alveoli, bood
• • Trachea: a tube which is supported by c-shaped rings of cartilage which prevents kinking
• Trachea: contains smooth muscles and elastic tissue which allows for constriction and recoil
• Bronchi and Bronchioles: have similar structures to the trachea. Bronchioles have no cartilage or ciliated epithelial cells; do not contain muscle that can contract to control their movement
• Alveoli: the lining of the alveolus is composed of flattened epethelial cells. Surrounded by collagen and elastic tissue- allows for stretching and recoil during breathing. Surrounded by a dense capillary network
• Oxygen moves by diffusion from the alveolar air down the concentration gradient into red blood cells. Carbon dioxide moves down he concentration gradient in opposite direction.
• Feature of exchange surface in capillaries: large surface area, short distance for diffusion, steep concentration gradient, more time of diffusion and moist alveolar surface.
• Inspiration: external intercostal muscles contractions, internal intercostal muscles relax, diaphragm contracts and flattens, volume of thorax increases as ribcage moves up and out, pressure of thorax decreases so air is forced into the lungs
• expiration: external intercostal muscles relax, internal intercostal muscles contract, diaphragm relaxed, volume of thorax decreases as ribcage moves in and down, pressure in thorax increases so air if forced out
• pulmonary ventilation= ventilation rate x tidal volume
• pulmonary ventilation= is the volume of air breathed in per minute
• ventilation rate= number of breaths per minute
• tidal volume= volume of one breath
• Risk factors= smoking, air pollution, genetics, infections and occupations
• ingestion: taking large pieces of food into the body
• digestion: hydrolysis of large insoluble molecules into small, soluble molecules
• absorption: taking up the soluble digestion products into the body cells
• Assimilation: using the absorbed materials in the body
• Egestion: eliminating the undigested materials
• Physical breakdown: large food molecules are broken down into smaller pieces by teeth. This allows for ingestion and provides a larger surface area for chemical digestion
• Chemical digestion: requires enzymes and hydrolysis to break down large molecules into smaller ones
• Carbohydrate digestion: polysaccharides and disaccharides are digested into monosaccharides by hydrolysis of glycosidic bonds
• Transpiration: the loss of water vapour through the stomata by evaporation
• key conditions of transpiration: light intensity, temperature, wind and humidity
• light intensity: more light causes stomata to open so larger surface area for evaporation
• temperature: more heat means more kinetic energy and faster moving molecules and therefore more evaporation
• wind: more wind will blow away humid air containing water vapour therefore maintaining the water gradient
• humidity: more water vapour in the air will make the water potential more positive outside the leaf, therefore reduces the water potential
• water moves up plant from the roots against gravity. This could be several metres against gravity in trees so that's why we have the cohesion tension theory
• COHESION: water is a dipolar molecule( slightly negative oxygen and slightly positive hydrogen) which enables hydrogen bonds to form between the hydrogen and oxygen of different molecules so it creates tension between water molecules so they stick together. Therefore water travels up he xylem as a continuous water column.
• CAPILLARITY: Adhesion of water is when water sticks to the molecules. Water adheres to the xylem walls. The narrower the xylem the bigger the impact of capillarity
• ROOT PRESSURE: as water moves into the roots by osmosis it increases the volume of liquid inside the root and therefore the pressure inside the root increases. This increase in pressure in the roots forces water above it upwards(positive pressure)
• cohesion+ adhesion+ root pressure= cohesion tension theory.
• gas exchange in plants: oxygen diffuses out of the stomata, carbon dioxide diffuses in through the stomata and to reduce water loss by evaporation stomata close at night when photosynthesis wouldn't be occurring.
• xerophytes are adapted to survive in environments with limited water