What substance can move across a barrier by osmosis? give the name, not the formula.
Show 1 The basic structure of a membrane is a 7 nm thick phospholipid bilayer with protein molecules 2 Phospholipid bilayers are a barrier to most watersoluble substances because the interior of the 3 Cholesterol is needed for membrane fluidity and stability. 4 Some proteins are transport proteins, transporting molecules or ions across the membrane. They may be either channel proteins or carrier proteins. Channel proteins have a fixed shape; carrier proteins change shape. 5 Some proteins act as enzymes – for example, in the cell surface membranes of microvilli in the gut. 6 Glycolipids and glycoproteins form receptors – for example, for hormones or neurotransmitters. 7 The cell surface membrane controls exchange between the cell and its environment. 8 Some chemical reactions take place on membranes inside cell organelles, as in photosynthesis and 9 Diffusion is the net movement of molecules or ions from a region of their higher concentration to one 10 Diffusion of ions and larger polar molecules through membranes is allowed by transport proteins. This process is called facilitated diff usion. 11 Water moves from regions of higher water potential to regions of lower water potential. When this takes place through a partially permeable membrane such as the cell surface membrane, this diff usion is called osmosis. 12 Pure water has a water potential (ψ) of zero. Adding solute reduces the water potential by an The following equation is used: ψ = ψp + pψs 13 In dilute solutions, animal cells burst as water moves into the cytoplasm from the solution. In dilute 14 Some ions and molecules move across membranes by active transport, against the concentration gradient. This needs a carrier protein and ATP to provide energy. 15 Exocytosis and endocytosis
involve the formation of vacuoles to move larger quantities of materials Multiple - choice Test 1 The diagram shows a small part of a cell surface membrane. Which regions are hydrophobic? A 1 and 2 only 2 The diagram shows part of a cell surface membrane. In addition to the molecules shown, cholesterol is also present. In which region is cholesterol found? 3 Which component of a cell surface membrane allows the movement of ions across the membrane? A cholesterol 4 The molecules which make up biological membranes have different functions. Which row matches molecules with their functions? 5 A substance moves into a cell through a protein pore. Which of the following describes this movement? A an ion moving against its concentration gradient by active transport 6 Which of the following correctly describes the movement of water by osmosis? A from a region of higher water potential to a region of lower water potential through a
fully permeable membrane 7 Which of the processes that transport materials across a cell surface membrane require energy from the cell’s supply of ATP? 8 A protein is synthesised by a ribosome in an animal cell. What is the sequence of events leading to the secretion of the protein by exocytosis? 1 protein modified by the Golgi apparatus A 1 → 2 → 5 → 4 → 3 9 Examples of the bulk transport of materials into or out of cells are listed. 1 white blood cell engulfing a bacterium Which are examples of exocytosis? A 1 and 2 only 10 A small piece of plant tissue was placed into each of three solutions, P, Q and R. After one hour, the tissues were examined using a light microscope and the appearance of the cells was recorded. What conclusion can be made about the water potentials of the three solutions? A The water potential of P is greater than that of R. Answers for Multiple - choice Test End-of-chapter questions 1 Whatare the most abundant molecules in the cell surface membranes of plant cells? 3 The cells of the myelin sheath are wrapped in layers around nerve cell axons. Freeze-fractured
preparations of themyelin sheath cell surface membranes show very few particles. This indicates that myelin membranes contain relativelfyew of which type of molecule? 4 Prepare a table to summarise briefly the major functions of phospholipids, cholesterol, glycolipids, glycoproteins and proteins in cell surface membranes. 5 a Describe fully what will occur if a plant cell is placed in a solution that has a higher water potential than the cell. Use the following terms in your answer. cell wall, freely permeable, partially permeable, cell surface membrane, vacuole, tonoplast, cytoplasm, solute potential, pressure potential, water potential, turgid, osmosis, protoplast, equilibrium b Describe fully what will occur if a plant cell is placedin a solution that has a lower water potential than the cell. Use the following terms in your answer. cell wall, freely permeable, partially permeable, cell surface membrane, vacuole, tonoplast, cytoplasm, solute potential, pressure potential, water potential, incipient plasmolysis, plasmolysed, osmosis, protoplast, equilibrium 6 The diagram shows part of a membrane containing a channel protein. Part of the protein molecule is shaded. a Identify the parts labelled A, Band C. 7 Copy the table below and place a tick or cross in each box as appropriate. 8 Copy and complete the table below to compare cell walls with cell membranes. 9 A cell with a water potential of -300 kPa was placed in pure water at time zero. The rate of entry of water into the cell was measured as the change in water potential with time. The graph shows the results of
this investigation. 10 The rate of movement of molecules or ions across a cell surface membrane is affected by the relative concentrations of themolecules or ions on either side of the membrane. The graphs below show the effect of concentration difference (the steepness of the concentration gradient) on three transport processes, namely diffusion, facilitated diffusion and activetransport. a With reference to the graphs, state what the three transport processes have in common.[1] [Total: 12] 11 When a cell gains or loses water, its volume changes. The graphs overleaf show changes in the water potential (Ψ), pressure potential (Ψ) and solute potential (Ψ) of a plant cell as its volume changes as a result of gaining or losing water. (Note that 80% relative cell volume means the cell or protoplast has shrunk to 80% of the volume it was at 100% relative cell volume.) a What is a protoplast? [1] b What is the pressure potential at 90%, 95% and 100% relative cell volume? [1] ii Calculate the change in pressure potential between 90% and 95% relative cell volume and between 95% and 100% relative cell volume,[2] iii Explain why the pressure potential curve is not linear.[2] iv State the water potential when the cell reaches maximum turgidity.[1] The graph shows that as the cell loses water, pressure potential falls and the relative cell volume decreases (the cell shrinks), c i What is the minimum value of the pressure potential? [1] ii In a shrinking cell, what is the relative cell volume when the minimum value of the pressure potential is reached? [1] iii What is the term used to describe the state of the cell at this point? [1] iv What happens to the values of water potential and solute potential at this point? [1] v State the equation which links Ψ p, Ψs and Ψ.[1] vi Describe what is happening to the cell between the point identified in c ii and c iii above and 80% relative cell volume.[5] d As the cell changes volume, the change in solute potential is much less than the change in pressure potential. Suggest an explanation for this.[3] [Total: 20] 12 Thediagram shows the concentration in mmol dm-3 of two different ions inside a human red blood cell and in the plasmaoutside the cell. a Explain why these concentrations could not have occurred as a result of diffusion.[1] b Explain how these concentrations could have been achieved.[2] c If respiration of red blood cells is inhibited, the concentrations of potassium and sodium ions inside the cells gradually change until they come into equilibrium with the plasma. Explain this observation.[4] [Total: 7] End-of-chapter answers 1 C N.B. It could be argued that facilitated diff usion is controllable, because the number of channel proteins in the membrane can aff ect the rate. Exam-style questions
Explanation cell wall rigid/will not stretch (far), and prevents entry of more water; cell is turgid; [max. 5] [Total: 8] 10 a the greater the concentration diff erence, the greater the rate of transport; [1] d graph for diff usion is linear/straight line (with no maximum rate); [Total: 12] 11 a the living contents of a plant cell; [1] [Total: 20]
[Total: 7] What substance can move across a barrier by osmosis?Whereas diffusion transports material across membranes and within cells, osmosis transports only water across a membrane and the membrane limits the diffusion of solutes in the water.
What substances are moved by osmosis?The only substance that carries out osmosis is water. Osmosis is the process of transferring water (solvent) through the semipermeable membrane. The process of movement of the water (solvent) molecules from the higher to lower solvent concentration region takes place in the osmosis transport mechanism.
Which substance is moved by osmosis but not diffusion?In biology, this is a difference between the two processes. One big difference between osmosis and diffusion is that both solvent and solute particles are free to move in diffusion, but when we talk about osmosis, only the solvent molecules (water molecules) cross the membrane.
What molecules during osmosis does not move across the membrane name one example?Molecules that cannot easily pass through the bilayer include ions and small hydrophilic molecules, such as glucose, and macromolecules, including proteins and RNA. Examples of molecules that can easily diffuse across the plasma membrane include carbon dioxide and oxygen gas.
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