Biology Unit 18: Cell Membranes and Movement Student Notes 2023 PDF

Biology Unit 18: Cell membranes and Movement Name: In this unit, students will build on their previous knowledge of cells to develop their knowledge of Movement of particles across the cell membrane. Gas exchange system. The movement of oxygen in living things This unit sho...

Biology Unit 18: Cell membranes and Movement Name: In this unit, students will build on their previous knowledge of cells to develop their knowledge of Movement of particles across the cell membrane. Gas exchange system. The movement of oxygen in living things This unit should take approximately three weeks to complete Objective: Review Form 3 Cells topic Review MRS GREN and describe the importance of cells as the smallest unit of life Describe basic cell Structure Describe the relationship between cells, organs and tissues Objective: Describe the movement of particles across cell membranes Define the role of the cell membrane. Note: Structure of the membrane not required Describe how the movement of molecules is required so that the cell can carry out its function Movement of molecules is restricted to oxygen, carbon dioxide, water, glucose and mineral ions Define diffusion as the net movement of particles from an area of high concentration to an area of low concentration. Define osmosis as the net movement of water molecules from a region of high water potential to an area of low water potential through a partially permeable membrane Define active transport as the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy Objective: Describe the gas exchange system in humans Define gas exchange, breathing and respiration and describe the differences between them Identify and place the organs and structures involved with the gas exchange system- nose, mouth, trachea, bronchi, bronchioles, alveoli, lungs, intercostal muscles, pleural membrane Objective: Describe the movement of oxygen in living things Name the major parts of the circulatory system: Heart, left and right ventricles and atria, pulmonary artery, pulmonary vein, aorta, vena cava, arteries, veins and capillaries. Discuss the link between the circulatory and respiratory systems Describe the role of Heart, lung, artery, vein, capillary, lungs, trachea, bronchiole, bronchus, alveolus in the movement of oxygen. Form 4 Unit 18 Cell membranes and Movement 2023 Page 1 Definitions: (Whakamāramatanga) Diffusion (ingo): the net movement of particles from an area of high concentration to an area of low concentration. Osmosis (rerewai): the net movement of water molecules from a region of high water potential to an area of low water potential through a partially permeable membrane. Active transport: the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy. Photosynthesis (ahotakakame): is the process by which plants, and some bacteria, synthesise food molecules – which they then use, in addition to other things, for respiration. The process of photosynthesis requires energy – it is endothermic. Respiration (tukupūngao): The chemical processes that break down nutrient molecules in living cells to release energy. Gas Exchange: A physical process in which the gas, oxygen, (needed for respiration) is exchanged for carbon dioxide (produced in respiration) across a membrane surface. Maori translations from https://paekupu.co.nz/ - Ministry of Education & https://maoridictionary.co.nz Form 4 Unit 15 Cell membranes and Movement 2023 Page 2 Objective: Review Form 3 Cells topic Characteristics of living organisms Living organisms have the following characteristics in common: Movement - they can move and change their position. Reproduction – they can make more of the same kind of organism as themselves. Sensitivity – they can detect or sense stimuli and respond to them. Growth - they can permanently increase their size or dry mass by increasing the number or size of their cells. Respiration – they can create chemical reactions that break down nutrient molecules in living cells to release energy. Excretion – they can excrete toxic materials, waste products of metabolism, and excess substances (note that excretion is not the same as egestion). Nutrition - they can take in and absorb nutrients such as organic substances and mineral ions. These nutrients contain the raw materials or energy needed for growth and tissue repair. The first letter of each of these characteristics makes up the acronym ‘MRS GREN’. This is a good way of remembering them. Living organisms can also control their internal conditions, such as their temperature or water content. Animals Animals are multicellular organisms – they consist of many cells that work together. Examples of animals include mammals (such as humans) and insects (such as houseflies and mosquitoes). Animal cell structure The main parts of an animal cell are the nucleus, cell membrane and cytoplasm. Animal cells:  do not have cell walls  do not contain chloroplasts, so animals cannot carry out photosynthesis  may store carbohydrate as glycogen Animals usually have nerves or nervous systems for coordination, and they are able to move from place to place. Form 4 Unit 15 Cell membranes and Movement 2023 Page 3 Plants Plants are also multicellular organisms – they consist of many cells that work together. Examples include cereals (such as maize), and peas and beans. Plant cell structure Plant cells contain the same parts as animal cells. They also have some additional ones:  chloroplasts  cell wall made of cellulose  permanent vacuole Other features of plants Plant cells contain chloroplasts so plants can carry out photosynthesis. They store carbohydrates as starch or sucrose. Cell structures and their functions Function Cytoplasm A jelly-like material that contains dissolved nutrients and salts and structures called organelles. It is where many of the chemical reactions happen. Nucleus Contains genetic material, including DNA. Cell membrane Controls the movement of substances in and out of the cell. Mitochondria Organelles that contain the enzymes for aerobic respiration, and where most energy is released in respiration. Ribosomes Site of protein synthesis. Most cells are specialised and are adapted for their function. Animals and plants therefore consist of many different types of cell working together. Form 4 Unit 15 Cell membranes and Movement 2023 Page 4 Plant cells also have additional structures: Function Chloroplast Organelles that contains the green pigment, chlorophyll, which absorbs light energy for photosynthesis. Contains the enzymes needed for photosynthesis. Cell wall Made from cellulose fibres and strengthens the cell and supports the plant. Permanent vacuole Filled with cell sap to help keep the cell turgid. Animal cells may also have vacuoles, but these are small and temporary. In animals, they are commonly used to store or transport substances. Cells and their functions Humans are multicellular. That means we are made of lots of cells, not just one cell. The cells in many multicellular animals and plants are specialised, so that they can share out the processes of life. They work together like a team to support the different processes in an organism. Cells, tissues, organs and systems Multicellular organisms are organised into increasingly complex parts. In order, from least complex to most complex: 1. cells 2. tissues 3. organs 4. organ systems 5. organism Tissues Animal cells and plant cells can form tissues, such as muscle tissue in animals. A living tissue is made from a group of cells with a similar structure and function, which all work together to do a particular job. Here are some examples of tissues:  muscle  the lining of the intestine  the lining of the lungs  xylem (tubes that carry water in a plant) Organs An organ is made from a group of different tissues, which all work together to do a particular job. Here are some examples of organs:  heart  lung  stomach  brain  leaf  root Form 4 Unit 15 Cell membranes and Movement 2023 Page 5 Organ systems An organ system is made from a group of different organs, which all work together to do a particular job. Here are some examples of organ systems:  circulatory system  respiratory system  digestive system  nervous system  reproductive system It must be remembered that cells are very small, and that many cells of the same type are usually arranged into groups called tissues to carry out a particular role. This is called specialisation. make up make up make up CELLS > TISSUES > ORGANS > INDIVIDUALS Objective: Describe the movement of particles across cell membranes Transport in cells For an organism to function, substances must move into and out of cells. Three processes contribute to this movement – diffusion, osmosis and active transport. Diffusion Particles (molecules and ions) in a liquid and a gas move continuously. Because of this movement, particles will spread themselves evenly throughout a liquid or a gas. If there is a situation where particles of a substance are in a higher concentration, they will move from this region to where they are in a lower concentration. This is called diffusion. It is important to remember that the particles:  will move in both directions, but there will be a net movement from high to low concentration  will end up evenly spread throughout the liquid or gas, but will continue to move Some examples of diffusion in biological systems Some substances move into and out of living cells by diffusion. e.g. in a leaf Form 4 Unit 15 Cell membranes and Movement 2023 Page 6 e.g. in a lung e.g. in the liver *Diffusion: the net movement of molecules from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement. Osmosis Osmosis is defined as the net movement of water molecules from a region of high water potential to an area of low water potential through a partially permeable membrane A dilute solution contains a high potential (higher number) of water molecules, while a concentrated solution contains a low potential (lower number) water molecules. Osmosis refers to the movement of water molecules only. The diagram on the next page shows an example of osmosis showing the direction of movement of water between two different potentials (concentrations) of sugar solutions. Form 4 Unit 15 Cell membranes and Movement 2023 Page 7 Step one Step two The beaker contains water and sugar molecules Water molecules pass through from solution one to two When the concentration of water is the same on both sides of the membrane, the movement of water molecules will be the same in both directions. There will be no net movement of water molecules. In theory, the level of solution two will rise, but this will be opposed by gravity and will be dependent on the width of the container. Similar observations will be made with solutions containing different solutes, for instance, salt instead of sugar. Osmosis across living cells Cells contain dilute solutions of ions, sugars and amino acids. The cell membrane is partially permeable. Water will move into and out of cells by osmosis. Plant cells Isolated plant cells placed in a dilute solution or water will take in water by osmosis. Root hair cells, if the soil is wet or moist, will also take up water by osmosis. Leaf cells of land plants, unless it is raining or the humidity is high, will have a tendency to lose water. Plant cells have a strong cellulose cell wall outside the cell membrane. The cell wall is fully permeable to all molecules and supports the cell and stops it bursting when it gains water by osmosis. Form 4 Unit 15 Cell membranes and Movement 2023 Page 8 If plant cells are placed in solutions of increasing solute concentration: (1) Pure water View of a plant cell In pure water, the cell contents (the cytoplasm and vacuole) push against the cell wall and the cell becomes turgid. Fully turgid cells support the stems of non-woody plants. (2) Concentrated solution In a more concentrated solution, the cell contents lose water by osmosis. They shrink and pull away from the cell wall. The cell becomes flaccid. It is becoming plasmolysed. (3) Highly-concentrated solution In a very concentrated solution, the cell undergoes full plasmolysis as the cells lose more water. Plants would be exposed to higher concentrations of solutes if there was less water in the soil - for instance, if plants were not watered, or plants in drought conditions. Plant cells would then lose water by osmosis. Aquatic, freshwater plants placed in the sea, or a seaweed in a rock pool where the water evaporated in the Sun, would also lose water by osmosis. Animal cells Animal cells also take in and lose water by osmosis. They do not have a cell wall, so will change size and shape when put into solutions that are at a different concentration to the cell contents. For example, red blood cells could:  lose water and shrink  gain water, swell and burst in a more dilute solution In animals, the concentration of body fluids – blood plasma and tissue fluid – must be kept within strict limits – if cells lose or gain too much water by osmosis, they do not function efficiently. Form 4 Unit 15 Cell membranes and Movement 2023 Page 9 Active transport Substances are transported passively down concentration gradients. Often, substances have to be moved from a low to a high concentration - against a concentration gradient. Active transport is a process that is required to move molecules against a concentration gradient. The process requires energy. Active transport in plants For plants to take up mineral ions, ions are moved into root hairs, where they are in a higher concentration than in the dilute solutions in the soil. Active transport then occurs across the root so that the plant takes in the ions it needs from the soil around it. Active transport in animals In animals, glucose molecules have to be moved across the gut wall into the blood. The glucose molecules in the intestine might be in a higher concentration than in the intestinal cells and blood – for instance, after a sugary meal – but there will be times when glucose concentration in the intestine might be lower. All the glucose in the gut needs to be absorbed. When the glucose concentration in the intestine is lower than in the intestinal cells, movement of glucose involves active transport. The process requires energy produced by respiration. Comparing diffusion, osmosis and active transport In animals, plants and microorganisms, substances move into and out of cells by diffusion, osmosis and active transport. Process Descriptions Substances moved Energy required Diffusion the net movement of particles from an Carbon dioxide, oxygen, No area of high concentration to an area of water, food substances, low concentration. wastes, e.g. urea Osmosis the net movement of water molecules Water No from a region of high water potential to an area of low water potential through a partially permeable membrane Active the movement of particles through a cell Mineral ions into plant roots, Yes transport membrane from a region of lower glucose from the gut into concentration to a region of higher intestinal cells, from where it concentration using energy moves into the blood Form 4 Unit 15 Cell membranes and Movement 2023 Page 10 Objective: Describe the gas exchange system in humans The Gas Exchange System. Gas Exchange: A physical process in which the gas, oxygen, (needed for respiration) is exchanged for carbon dioxide (produced in respiration) across a membrane surface. Exchanging gases A large part of your upper body, including most of your chest, is made up of structures that enable gases from the air to get into our blood and to get rid of waste gases from our body. These waste gases (mainly carbon dioxide) are produced by cellular respiration in the body’s cells and are then carried by the bloodstream to the lungs, where it is exchanged for oxygen. How does get air in? In mammals, breathing in, or inhaling, is due to the contraction and flattening of the diaphragm, a domed muscle that separates thorax and abdomen. If the abdomen is relaxed, this contraction causes the abdomen to bulge outwards, expanding the volume of the body. This increased volume causes a fall in pressure in the thorax, which causes the expansion of the lungs. Air is then sucked* into the lungs. When the diaphragm relaxes, air leaves largely by elasticity of the lung. This is quiet, relaxed breathing needing little energy. When need increases, the abdominal muscles resist expansion. The increased abdominal pressure then tilts the diaphragm and ribcage upwards with an increase in volume and the entry of air. Expiration follows relaxation of diaphragm and abdominal muscles, but can be increased by downward action of abdominal muscles on the rib cage. Once the air is in the alveoli, some of the oxygen moves into the blood vessels through the walls of the alveoli, and some carbon dioxide moves out. The alveoli provide a very large surface area for the exchange of gases between the lungs and the blood system. If all the alveoli in the lungs were spread out they would cover the surface of a tennis court. *The process of suction is a misnomer. It is because the pressure in the lung is less than the pressure of the atmosphere and so air is forced into the lungs from outside. Laboratory simulation of diaphragm action during breathing. Form 4 Unit 15 Cell membranes and Movement 2023 Page 11 Respiration* *Respiration: The chemical processes that break down nutrient molecules in living cells to release energy. Form 4 Unit 15 Cell membranes and Movement 2023 Page 12 Cellular respiration Respiration releases energy – it is an exothermic process. It releases heat energy. Don't confuse respiration with breathing, which is ventilation. Respiration happens in cells. Why organisms need energy All organisms need energy to live. This energy is used:  to drive the chemical reactions needed to keep organisms alive – the reactions to build complex carbohydrates, proteins and lipids from the products of photosynthesis in plants, and the products of digestion in animals, require energy  movement – in animals, energy is needed to make muscles contract, while in plants, it is needed for transport of substances in the phloem Respiration is only around 40 per cent efficient. As animals respire, heat is also released. In birds and mammals, this heat is distributed around the body by the blood. It keeps these animals warm and helps to keep a constant internal temperature. Energy is also used:  for cell division  to maintain constant conditions in cells and the body – homeostasis  to move molecules against concentration gradients in active transport  for the transmission of nerve impulses Aerobic respiration Respiration using oxygen to break down food molecules is called aerobic respiration. Glucose is the molecule normally used for respiration – it is the main respiratory substrate. Glucose is oxidised to release its energy. The word equation for aerobic respiration is: glucose + oxygen → carbon dioxide + water + energy released You need to be able to recognise the chemical symbols: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy released Respiration is a series of reactions, but this summarises the overall process. The first stages of respiration occur in the cytoplasm of cells, but most of the energy released is in the mitochondria. Glucose + oxygen → carbon dioxide + water + energy Form 4 Unit 15 Cell membranes and Movement 2023 Page 13 Objective: Describe the movement of oxygen in living things Our Circulatory System. Animals need a transport system to move materials to all parts of their body more quickly than by diffusion alone. Their circulatory system consists of a pump (the heart), and blood vessels, namely arteries, veins and capillaries in which the blood flows. They have a double circulation system, which keeps the blood rich in oxygen and food separate from the blood low in oxygen and food. The blood circulates continuously in the following sequence: heart arteries capillary network within an organism vein heart The exchange of materials between the blood and the cells takes place through the walls of the capillaries via the tissue fluid. Please note that students are only expected to know the following for examinations Pulmonary vein Pulmonary artery Aorta Vena Cava Blood vessels Arteries These vessels carry blood from the heart to the other organs of the body. They have thick, elastic and muscular walls. They need to be strong to withstand the high pressure each time the heart pumps blood into them. Veins These are blood vessels, which carry blood from the body's organs towards the heart. Veins have thinner, less muscular and less elastic walls than arteries. The blood pressure is comparatively low and these vessels are lined with valves, which prevent the back flow of blood. Form 4 Unit 15 Cell membranes and Movement 2023 Page 14 Capillaries These make up the bulk of the body's blood vessels. They form a network through every tissue and are in close contact with every cell. Capillaries are tiny vessels with very thin walls. The key task of the circulatory system, namely the exchange of materials between cells and blood, takes place through capillaries. The Heart It is a muscular organ about the size of a closed fist and its main function is to pump the blood around the body. It is actually a double pump with the following features: Right Atrium Left Atrium Right Ventricle Left Ventricle On the diagram label the following: Aorta, Vena cava, Pulmonary artery and pulmonary vein 1. The left and right atria collect the blood coming from the lungs and body. 2. The left and right ventricles, which have thick muscular walls for pumping the blood to the lungs and body. 3. Valves to stop the blood from flowing back into the auricles. The heart responds to the needs of the body. Example: in a human adult at rest, it beats at a rate of about 70-75 per minute, but this rate may double during strenuous exercise. Form 4 Unit 15 Cell membranes and Movement 2023 Page 15 Experiment 15.1 The Diffusion of Starch and Glucose Teacher Demonstration [Kit 15.1] Introduction: How does digested food pass through the intestine wall and into the blood stream? Although the actual process depends on the type of nutrient, a fair amount of transfer occurs through the process of diffusion. Question / Aim: (What are you trying to find out?) To observe the diffusion of starch and glucose through a partially permeable membrane. Equipment: (What will you use?) Safety glasses, Dialysis tube ~ 10 cm long ( this is a partially-permeable substance), Large beaker (250 mL) of warm water (~35 0C) ,Glucose/starch solution, Iodine solution for starch test, Benedict’s solution for glucose test, Syringe Method: (How will you use the equipment?) 1. Moisten the dialysis tube and rub with fingers to free both surfaces. 2. Tie one end of dialysis tube tightly. 3. Fill with glucose/starch solution. 4. Tie other end securely (knot with string if necessary), and rinse in cold water. 5. Now place in the large beaker of warm water and leave for ~ 30-40 mins 6. Using the syringe, withdraw 2mL of water in contact with the dialysis tube and test for glucose (Benedict’s). 7. Repeat this step and test for starch (iodine). Results: (What information did you collect?) Glucose test Starch test Conclusion: Form 4 Unit 15 Cell membranes and Movement 2023 Page 16 Discussion: (a) Explain in your own words what has happened. (b) Why can’t the starch pass through the dialysis tubing into the water? (c) What then does semi-permeable mean? (d) In what ways does this experiment model what happens in your small intestine? (e) In what way does it differ? (f) Give a definition of diffusion. Conclusion: (g) Write a brief conclusion. Form 4 Unit 15 Cell membranes and Movement 2023 Page 17 Experiment 15.2 - Surface Area to volume ratio [Kit 15.2] Introduction: In this investigation, we will work with different sized blocks of agar (a chemical extracted from sea weed) which has been mixed with phenolphthalein (an indicator that goes bright pink with a base and colourless with an acid.) The colour change will show us how far the molecules have penetrated or diffused into the different-sized blocks. Aim / Question: (What are you trying to find out?) To investigate the relationship between cell size and diffusion, and to relate this to the surface area to volume (SA / Vol) ratio. Equipment: (What will you use?) Agar-phenolphthalein blocks – cut to size, 4% sodium hydroxide solution, knife, ruler, beaker, stopwatch, plastic spoons (to lift the blocks out of the beaker) and Paper Towels. Method: (How will you use the equipment?) 1. Using the knife, cut three blocks from the agar: one 3x3x3 cm, one 2x2x2 cm, and one 1x1x1 cm. (Cut the big one first so that you don’t run out of agar!) 2. Place the three cubes into a beaker and cover with sodium hydroxide. Note the time. 3. While the cubes are soaking, work out the surface area and volume for each block, and the SA / Vol ratio by completing the table in the results section. 4. After 10 minutes, remove the blocks with the plastic spoons and place them on a paper towel. Blot them dry. 5. Cut through the middle of each block. Wipe the blade of the knife between each cut so that you do not smear NaOH (sodium hydroxide) onto the surface of the next block. 6. Measure the length of the cube that has not been coloured (h). This way you are indirectly measuring the distance that the NaOH has diffused into the block. Record results in table below. Results: (What information did you collect?) Length Surface Volume Simplest Length of Extent Volume not Volume % of area, A B, ratio of cube not of penetrated penetrated Penetration cube (lxwx6) (lxwxH) A/B penetrated diffusion (hxhxh) = B – NP = P P/B x side, H (h) (H – h) NP 100/1 3cm 2cm 1cm Analysis: Using the graph paper on the next page plot a graph with percentage penetration on the vertical axis and the SA / Vol ratio on the horizontal axis. Discussion: 1. Which cell had the greatest SA / Vol ratio? 2. Was there diffusion in two directions? Explain from your observations (hint look at your beaker of NaOH) 3. How does a plant cell overcome the problem of being a larger cell? And why do you think the chloroplasts are found around the edge of the cell? Form 4 Unit 15 Cell membranes and Movement 2023 Page 18 Analysis: Using the graph paper on the next page plot a graph with percentage penetration on the vertical axis and the SA / Vol ratio on the horizontal axis. Form 4 Unit 15 Cell membranes and Movement 2023 Page 19 Experiment 15.3 – Osmosis in potato cells [Kit 15.3] Teacher Demonstration Introduction: The process of osmosis causes water to pass into (and sometimes out of) cells. If water is lost from plant cells, the cells are said to be plasmolysed whereas cells that have gained water are said to be turgid. Aim / Question: (What are you trying to find out?) How does the concentration of sugar solutions effect Osmosis in potato cells? Equipment: (What will you use?) Water, solid sugar, electronic balance, measuring cylinder, five test tubes, test tube rack, raw potatoes, knife, chopping board, paper towels. Method: (How will you use the equipment?) 1. Mix up sugar solutions of different concentrations as follows: 0.1 Molar = 3.4g sucrose in 100mL water 0.3 Molar = 10.3g sucrose in 100mL water 0.5 Molar = 17.1g sucrose in 100mL water 0.7 Molar = 23.9g sucrose in 100mL water 2. Label five test-tubes. Add a different sugar solution to four of the vials and water to the fifth 3. Cut five equal sized ‘chips’ from a raw potato, or use a cork borer to cut round ‘chips’. 4. Weigh each ‘chip’ and place it in one of the test-tubes. Keep a record of the original weight of the potato ‘chip’ in each test-tube by filling in the results table. 5. Leave the test-tubes for 24 hours and then remove each ‘chip’ blot dry and reweigh. 6. Use the following formula to calculate the percentage weight change for each ‘chip’ Percentage weight change = difference in weight x 100 original weight 7. Tabulate and graph your results Results: (What information did you collect?) Potato Sample Initial Weight (g) Concentration of Reweigh after Percentage weight sugar solutions 24hrs (g) change % (mol) 1 2 3 4 5 Form 4 Unit 15 Cell membranes and Movement 2023 Page 20 Analysis: 1. Plot percentage Weight Gain on the vertical axis and sucrose concentration on the horizontal axis. 2. Use your graph to estimate the water concentration inside the potato cells 3. Explain your results in terms of osmosis. Form 4 Unit 15 Cell membranes and Movement 2023 Page 21