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B4 – Homeostasis. Overview of Topic. Diffusion & Active transport Osmosis Enzymes & optimum temperature Control and Feedback systems Homeostasis and temperature What happens if you get too hot or too cold? Homeostasis and water balance Hormones and water balance Kidneys. Objectives.
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Overview of Topic • Diffusion & Active transport • Osmosis • Enzymes & optimum temperature • Control and Feedback systems • Homeostasis and temperature • What happens if you get too hot or too cold? • Homeostasis and water balance • Hormones and water balance • Kidneys
Objectives • Explain how diffusion and active transport work
Smells and liquids spreading out Why can you smell cooked food from a distance? Why does the colour of concentrated fruit drink change when it is added to water? Why can you smell perfume or aftershave when someone walks past you?
Diffusion • Diffusion is the net movement of particles from a region of high concentration to a region of low concentration (concentration gradient). • Only happens in gases or a substance in solution. • It occurs because the particles move around and bump into each other and begin to spread out.
high concentration low concentration Changing concentrations During diffusion molecules move from an area of high concentration to an area of low concentration often through a partially permeable membrane. Diffusion is a passive process which means that no energy is needed. Molecules diffuse until they are evenly spaced apart and equilibrium is reached.
Concentration Gradient • The difference between the concentration in each area is called the concentration gradient. • The bigger the concentration gradient the faster the rate of diffusion will occur. WHAT ELSE DO YOU THINK WOULD AFFECT THE RATE OF DIFFUSION?
Net Movement • At lower concentration gradients the rate appears slower because particles from the other side may be moving too. • Because particles may move from either side we must consider the net movement of particles. • Net movement = particles moving in - particles moving out
Why is diffusion so important? Diffusion is an essential process that is going on inside your body right now and keeping you alive! Diffusion occurs in the organ systems that control your breathing, circulation, digestion and other life processes.
Active Transport • Active transport is the opposite to diffusion. • Its when particles move from a region of low concentration to a region of high concentration. • It requires energy to do this as it is going against the concentration gradient. high concentration diffusion active transport low concentration
What is active transport? Substances can move passively in and out of cells by diffusion until the concentration on both sides of the cell membrane reaches an equilibrium. Once they have reached equilibrium they will not appear to move anymore. Substances can continue to move in and out of a cell using a process called active transport. During active transport, protein carriers in the cell membrane ‘pick up’ particles and move them against the concentration gradient. As the name suggests, active transport requires energy from the cell, which is made available by respiration.
Questions • What is diffusion? • What is active transport? • What is the difference between diffusion and active transport? • What is a partially permeable membrane? • Why does oxygen diffuse into the blood from the lungs? • Why does food diffuse into the blood from the intestines?
Objectives • Explain how osmosis works
What is osmosis? water molecule Osmosis is a special type of diffusion. Diffusion involves gas or dissolved molecules, but osmosis only involves the movement of water molecules. Osmosis occurs across a semi-permeable membranewhich has tiny holes in it. These holes are small enough for water molecules to pass through but larger molecules cannot pass through.
What happens during osmosis? osmosis water molecule semipermeable membrane Osmosis is the movement of water molecules from a region of high water concentration(dilute sol’n) to a region of low water concentration (concsol’n) across a semi-permeable membrane.
pure water dilute solution concentrated solution Dilute vs. concentrated . • During osmosis, water molecules diffuse from pure water or dilute solution to more concentrated solutions • Dilute solutions have a high concentration of water molecules. • Concentrated solutions have a low concentration of water molecules.
Osmosis and animal cells Animal cells do not have a cell wall. This means they respond differently than plant cells to the gain and loss of water. In dilute solutions, water moves into the cell causing the cell to swell up and burst. This is called lysis. In concentrated solutions, water moves out from the cell from the cytoplasm, and causes the cells to shrivel and shrink.
Objectives • Describe what an enzyme is and what conditions they work best in
What are enzymes? • Enzymes are proteins. They are biological catalysts – they speed up the chemical reactions that take place inside all cells, but without being used up in the process. • There are many thousands of different types of enzyme, and each one catalyses (speeds up) a different reaction. • They are specific to each reaction due to their ‘lock and key’ structure.
The ‘Lock and Key’ model • Each enzyme binds to a specific molecule called the reactant or substrate. • The part of the enzyme to which the reactant binds is called the active site. It is a very specific shape and the most important part of the enzyme. • Only the substrate that matches the active site can bind to the enzyme. This is why we call it the lock and key model.
What happens at the active site? + + enzyme enzyme enzyme-substrate complex ↔ ↔ + + substrate products ↔ ↔
Why do enzymes speed up reactions? Ea without enzyme Ea with enzyme energy (kJ) reaction (time) Enzymes speed up reactions by lowering the activation energy (Ea) of a reaction. The activation energy is the energy needed to start a reaction. Different reactions have different activation energies.
How else can we speed up reactions? Another way to speed up chemical reactions is to increase the temperature. If the temperature gets too high though, the enzyme will stop working. Human body Optimum Temp = 37°C
Factors affecting enzymes heat pH normal denatured Enzymes work at an optimum temperature and pH. If the temperature and pH changes from an enzyme’s optimum level, the shape of the enzyme irreversibly changes. This affects the shape of the active site and means that the enzyme will no longer work. When this happens we call the enzyme denatured.
Enzyme Questions • What are enzymes also known as? • What do enzymes do to biological reactions? • What do we call the special shape on an enzyme molecule? • What are enzymes made of? • What is created when an enzyme and substrate combine together? • What is lost when an enzyme is denatured? • Write down two factors that can cause denaturing.
Enzyme Practical • Put 5cm starch solution and 1cm amylase (enzyme) in a boiling tube • Repeat this for 5 boiling tubes • Place each boiling tube in a different condition and leave for 15 minutes • Conditions are: • Ice(0°C), Room temp (20°C), 40°C, 60°C and 80°C. CAUTION – VERY HOT WATER!!
Enzyme Practical • After 15 minutes remove the test tube from the water bath and place in a test tube rack. • Then add a few drops of iodine to each solution and observe the reaction. • Record the results in a table. • See if you can draw any conclusions about the temperature amylase likes to work at.
Starter Activity • List your senses • Tick which ones you used coming into the room • How would you tell the temperature of a cup of water without a thermometer?
Objectives • Describe how a control and feedback system work
How does this greenhouse maintain its temperature? • If its too cold... • A receptor detects the temperature, which sends a message to a processing centre (computer), which triggers a response in the effector, which in this case turns heaters on • And if its too hot...A receptor detects the temperature, which sends a message to a processing centre (computer), which triggers a response in the effector, which in this case opens ventilation flaps to allow cooling.
The same thing happens in the human body STIMULUS is the change your body detects RECEPTORS in the body detect a change inside or outside of the body CENTRAL NERVOUS SYSTEM (CNS) co-ordinates the body’s response, made up of brain and spinal cord EFFECTORS cause a response by moving part of the body or secreting a hormone STIMULUS Friend shouts you RECEPTOR In your ears EFFECTOR Muscles contract so you turn to look at them (CNS) Example...
Write a control and feedback flow diagram for each of these situations • You touch a hot pan on a cooker • You prick your finger on something sharp • Your friends shouts your name and you turn round to look at them
What is the central nervous system? The central nervous system (CNS) is made up of the brain and spinal cord. cerebralhemisphere cerebellum spinalcord
What are reflexes? Reflexes are fast, automatic protective biological control systems that link a stimulus to a response. Reflex reactions happen without you having to think about them – they are involuntary. This is because the central nervous system (CNS) sends electrical signals to the muscles before the brain can pick up the message. Many reflexes such as sneezing and focusing your eyes occur naturally, but other reflexes can be learned, i.e. conditioned responses.
What are neurones? nerve nerve fibre Neurones are specialised cells that conduct electrical impulses through the body. A nerve is a bundle of many nerve fibres enclosed within a protective sheath. Nerve fibres are the long axons of neurones together with any associated tissues.
Definitions • Stimulus – Changes that receptor cells detect. • Receptors – Cells that detect changes inside or outside the body. • Sense organs – organs that contain receptor cells. • Effectors – Organs in the body that cause a response. They can be muscles or glands.
