Topic 3 - Movement In And Out Of Cells PDF

Chapter3 MOVEMENT INTO AND OUT OF CELLS 1 Describe diffusion as the net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement 2 State that the energy for diffusion comes fr...

Chapter3 MOVEMENT INTO AND OUT OF CELLS 1 Describe diffusion as the net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement 2 State that the energy for diffusion comes from the kinetic energy of random movement of molecules and ions 3 State that some substances move into and out of cells by diffusion through the cell membrane 4 Describe the importance of diffusion of gases and solutes in living organisms 5 Investigate the factors that influence diffusion, limited to: surface area, temperature, concentration gradient and distance 6 Describe the role of water as a solvent in organisms with reference to digestion, excretion and transport 7 State that water diffuses through partially permeable membranes by osmosis 8 State that water moves into and out of cells by osmosis through the cell membrane 9 Investigate osmosis using materials such as dialysis tubing 10 Investigate and describe the effects on plant tissues of immersing them in solutions of different concentrations 11 State that plants are supported by the pressure of water inside the cells pressing outwards on the cell wall 12 Describe active transport as the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (i.e. against a concentration gradient), using energy from respiration 23 Cell membranes are semi-permeable, meaning they have control over what molecules can or cannot pass through. Some molecules can just drift in and out, others require special structures to get in and out of a cell, while some molecules even need an energy boost to get across a cell membrane. Movement Across a Membrane and Energy There are two major ways that molecules can be moved across a membrane, and the distinction has to do with whether or not cell energy is used. Passive Active transport mechanisms use requires energy to no energy be done. Molecules 24 1 Diffusion Diffusion is the net movement of particles 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 The energy for diffusion comes from the kinetic energy of this random movement (Brownian motion) of molecules and ions Diffusion helps living organisms to: - Obtain many of their requirements - Get rid of many of their waste products - Carry out gas exchange for respiration Examples of diffusion in living organisms Site Molecules Moving From To Small intestine Digested food Blood/lymph in villi (glucose, amino acids, Lumen of small found covering the fatty acids, glycerol intestine (ileum) small intestine walls ….etc.) Mitochondria in the Air Leaf cells for respiration Oxygen The cells as a product Air of photosynthesis Carbon dioxide Air Chloroplasts Water vapour Stomata Air Lungs Oxygen Alveoli Blood Carbon dioxide Blood Alveoli 25  Factors affecting rate of diffusion # Factor Effect The greater the surface area, the higher the rate of diffusion. Many cells which are adapted for diffusion have increased surface area in some way – eg root hair cells in plants (which absorb water and Surface area mineral ions) and cells (villi) lining the ileum in animals (which absorb the 1 to volume products of digestion) ratio The higher the temperature, the faster molecules move, the higher the 2 Temperature rate of diffusion. The smaller the distance molecules have to travel the faster transport Diffusion will occur. 3 distance This is why blood capillaries and alveoli have walls which are only one cell thick. 26 Example from the past papers June 2004 QP - Paper 1 CIE Biology IGCSE 2 Osmosis Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane Semi-permeable/partially permeable membranes are those which only let solvents, such as water, pass through them. Permeable membranes are those which let solvents and solutes, such as ions and molecules, to pass through them. 27  Importance of Osmosis Water is moving down its concentration gradient. When water moves into a plant cell, the vacuole gets bigger, pushing the cell membrane against the cell wall. Water entering the cell by osmosis makes the cell rigid and firm. This is important for plants as the effect of all the cells in a plant being firm is to provide support and strength for the plant making the plant stand upright with its leaves held out to catch sunlight. The pressure created by the cell wall stops too much water entering and prevents the cell from bursting. If plants do not receive enough water the cells cannot remain rigid and firm (turgid) and the plant wilts. Animal cell => No cell wall to prevent bursting => A cell wall prevents bursting 28 Visking tube (dialysis tube) is a partially permeable membrane, smaller molecules like water and glucose pass through its microscopic holes, larger molecules like starch and sucrose cannot pass through it. 1 2 3 4 No change Water direction will Water direction will be Water direction will be into the visking also into the visking be to the outside of tube so its mass will tube so its mass will the visking tube so its increase increase even more as mass will decrease it contains more sucrose Practical Work Topic 3 (Osmosis Experiment) Example from the past papers June 2012 (v2) QP - Paper 2 CIE Biology IGCSE 3 29 3 Active Transport Active transport is the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration Energy is needed because particles are being moved against a concentration gradient, in the opposite direction from which they would naturally move (by diffusion) Examples of active transport include: - Uptake of glucose by the villi of the small intestine and by kidney tubules - Uptake of ions from soil water by root hair cells in plants Protein carrier Example from the past papers March 2018 (v2) QP - Paper 3 CIE Biology IGCSE 30