Grade 10 Study Guide for Q2-1 PDF

## The Human Gas Exchange System **Figure 11.3: The human gas exchange system.** **Alveoli** - There are many tiny air sacs or alveoli at the end of each bronchiole - This is where gas exchange takes place. - The walls of the alveoli are the gas exchange surface. - Tiny capillaries are closely wr...

## The Human Gas Exchange System **Figure 11.3: The human gas exchange system.** **Alveoli** - There are many tiny air sacs or alveoli at the end of each bronchiole - This is where gas exchange takes place. - The walls of the alveoli are the gas exchange surface. - Tiny capillaries are closely wrapped around the outside of the alveoli. - Oxygen diffuses across the walls of the alveoli into the blood. - Carbon dioxide diffuses the other way. - The walls of the alveoli have several features which make them an efficient gas exchange surface: - They are very thin. They are only one cell thick. - The capillary walls are also only one cell thick. **Summary** - Organisms need energy for muscle contraction, protein synthesis, cell division, active transport, growth, transmitting nerve impulses and maintaining a constant body temperature. - Respiration is a metabolic reaction that takes place in all living cells. - Respiration releases energy from glucose and other nutrient molecules. - Respiration, like all metabolic reactions, is controlled by enzymes. - In yeast, an increase in temperature causes an increase in the rate of respiration, but at temperatures above about 40°C, enzymes are denatured and so the rate decreases. - Aerobic respiration happens in mitochondria. Oxygen is combined with glucose, releasing a lot of energy and producing carbon dioxide and water. - Anaerobic respiration happens in the cytoplasm. Glucose is broken down without using oxygen. - Anaerobic respiration releases a small amount of energy. In humans, lactic acid is produced, and in yeast, carbon dioxide and ethanol are produced. - The place where oxygen enters an organism's body and carbon dioxide leaves is called the gas exchange surface. In terrestrial animals, these surfaces have a large surface area, a thin surface, a good blood supply and good ventilation with air. - In humans, the gas exchange surface is the alveoli in the lungs. Air moves to them through the trachea, bronchi and bronchioles. ## Coordination in Plants - Like animals, plants are able to respond to their environment. - Plants usually respond with much slower responses than those of animals. - In general, plants respond to stimuli by changing their rate or direction of growth. - They may grow either towards or away from a stimulus. - Growth towards a stimulus is said to be a positive response, and growth away from a stimulus is a negative response. - These growth responses are called tropisms. - Two important stimuli for plants are light and gravity. - Growth responses to light are called phototropism. - Growth responses to gravity are called gravitropism. - Shoots normally grow towards light. - They are positively phototropic. - Roots do not usually respond to light, but in some plants, the root grows away from light. ## The Nervous System - In mammals, the nervous system is made up of the central nervous system and the peripheral nervous system. - The nervous system coordinates and helps to regulate body functions. - Neurones transmit information in the form of electrical impulses. - A reflex arc consists of a sensory neurone, relay neurone and motor neurone. - An impulse produced in a receptor passes along the sensory neurone, into the relay neurone, then the motor neurone, and then to an effector. - The effector takes action, bringing about a reflex action. - Reflex actions are fast and automatic. - A place where two neurones meet is called a synapse. - The arrival of an electrical impulse in the first neurone at a synapse stimulates it to release molecules of neurotransmitter into the synaptic gap. - The neurotransmitter diffuses across the gap and binds with receptor proteins on the membrane of the second neurone. - This stimulates an electrical impulse in the second neurone. - As there is neurotransmitter on only one side at a synapse, the impulse can only cross the synapse in one direction. - Sense organs are groups of receptor cells that respond to specific stimuli. - In the eye, the cornea refracts (bends) light and the lens helps to focus light onto the retina, where receptor cells are found. - Some of these receptor cells are sensitive to light of different colours. - They produce electrical impulses that pass along the optic nerve to the brain. ## The Endocrine System - Hormones are chemicals that are produced by glands and travel in the blood. They alter the activity of target organs. - The adrenal glands secrete adrenaline, which prepares the body for fight or flight by increasing breathing rate, heart rate and the diameter of the pupil. - Adrenaline increases metabolic activity. - Adrenaline increases blood glucose concentration and the supply of glucose and oxygen to body organs by increasing heart rate and breathing rate. - Nervous control acts more quickly than hormonal control but lasts for a shorter time. ## Coordination in Plants - Plants respond to stimuli by growth. - Gravitropism is a growth response to gravity, and phototropism is a growth response to light. - Usually, shoots are positively phototropic and negatively gravitropic. - Roots are positively gravitropic and do not usually respond to light. - Tropic responses are controlled by auxin, which is secreted by cells in the tip of a shoot. - Auxin concentrates on the shady or lower side of a shoot, making the cells in those areas elongate faster than on the other side. - This causes the shoot to bend towards light or away from gravity as it grows.