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Transport

A-Level AQA Biology

This pack of flashcards covers the complex structure and functions of cell membranes and transport mechanisms. It explains the fluid-mosaic model, phospholipid bilayer arrangement, protein roles, diffusion processes, osmosis, isotonic solutions, and active transport, including co-transport involving sodium and glucose ions.

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"Describe the fluid-mosaic model of cell and organelle membranes."	"The fluid-mosaic model describes the structure of cell and organelle membranes as a mixture and movement of phospholipids, proteins, glycoproteins, and glycolipids. Cholesterol is also present in some membranes, restricting the lateral movement of other molecules in the membrane, making the membrane less fluid at high temperatures, and preventing water and dissolved ions from leaking out of the cell."
"How do phospholipids align in a cell membrane?"	"Phospholipids align as a bilayer in a cell membrane due to the hydrophilic heads being attracted to water and the hydrophobic tails being repelled by water."
"Define peripheral and integral proteins in the context of a cell membrane."	"Peripheral proteins in a cell membrane do not extend completely across the membrane and provide mechanical support or connect to proteins or lipids to make glycoproteins and glycolipids. Integral proteins span across from one side of the bilayer to the other and are involved in the transport of molecules across the membrane."
"Explain the role of protein channels and carrier proteins in a cell membrane."	"Protein channels in a cell membrane form tubes that fill with water to enable water-soluble ions to diffuse. Carrier proteins bind with other molecules and larger molecules, such as glucose and amino acids, and change shape to transport them to the other side of the membrane."
"What is a partially permeable membrane?"	"A partially permeable membrane is the cell-surface membrane created by the arrangement of molecules within the phospholipid bilayer. It allows certain molecules or ions to pass through it by diffusion."
"Define simple diffusion as a mode of transport in and out of cells."	"Simple diffusion is the net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached. It is one of the five key modes of transport in and out of cells."
"Describe the process of simple diffusion."	"Simple diffusion is a passive process that does not require ATP. Molecules move due to their kinetic energy, allowing them to constantly move in fluids. For molecules to diffuse across the membrane, they must be lipid-soluble and small. Examples of such molecules include oxygen and carbon dioxide."
"Define facilitated diffusion and how it differs from simple diffusion."	"Facilitated diffusion is also a passive process that does not require ATP, but it differs from simple diffusion as proteins are used to transport molecules. The movement of ions and polar molecules, which cannot simply diffuse, can be transported across membranes by facilitated diffusion using protein channels and carrier proteins."
"How do protein channels and carrier proteins function in facilitated diffusion?"	"Protein channels form tubes filled with water, enabling water-soluble ions to pass through the membrane. They only open in the presence of certain ions when they bind to the protein. Carrier proteins bind with a molecule, such as glucose, causing a change in the shape of the protein. This shape change enables the molecule to be released to the other side of the membrane."
"Define osmosis and explain the concept of water potential."	"Osmosis is the movement of water from an area of higher water potentials to an area of lower water potential across a partially permeable membrane. Water potential is the pressure created by water molecules, measured in kPa and represented with the symbol Ψ. Pure water has a water potential of zero, and when solutes are dissolved in water, the water potential becomes negative. The more negative the water potential, the more solute must be dissolved in it."
"What is an isotonic solution?"	"An isotonic solution is when the water potential is the same in the solution and the cell within the solution."
"What does it mean when a solution is hypotonic?"	"A solution is hypotonic when the water potential of the solution is more positive (closer to zero) than the cell."
"Define the term 'Hypertonic' in the context of cell biology."	"Hypertonic refers to a solution with a more negative water potential than the cell. In such a solution, both animal and plant cells will shrink and become shrivelled due to large volumes of water leaving the cell by osmosis."
"Describe what happens to an animal cell when placed in a hypotonic solution."	"When an animal cell is placed in a hypotonic solution such as pure water, a lot of water will move into the cell by osmosis. Since animal cells do not have a cell wall, the pressure will cause the cell to burst."
"Explain the process of active transport in cell biology."	"Active transport is the movement of molecules and ions from an area of lower concentration to an area of higher concentration (against the concentration gradient) using ATP and carrier proteins. The carrier proteins act as pumps to move substances across the membrane. This process is very selective, as only certain molecules can bind to the carrier proteins to be pumped."
"How does ATP and carrier proteins function in active transport?"	"Certain molecules can bind to the receptor site on carrier proteins. ATP binds to the protein on the inside of the membrane and is hydrolysed into ADP and Pi. This causes the protein to change shape and open towards the inside of the membrane, releasing the molecule on the other side. The Pi molecule is then released from the protein, causing the protein to revert to its original shape."
"Describe the process of co-transport in the context of sodium and glucose ions absorption."	"In co-transport, sodium ions are transported by active transport from the epithelial cells to the blood via a protein carrier. This lowers the concentration of sodium in the epithelial cell, creating a concentration gradient between the ileum and the epithelial cell."

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Describe the fluid-mosaic model of cell and organelle membranes.

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The fluid-mosaic model describes the structure of cell and organelle membranes as a mixture and movement of phospholipids, proteins, glycoproteins, and glycolipids. Cholesterol is also present in some membranes, restricting the lateral movement of other molecules in the membrane, making the membrane less fluid at high temperatures, and preventing water and dissolved ions from leaking out of the cell.

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[{"id":1275300,"front":"Describe the fluid-mosaic model of cell and organelle membranes.","back":"The fluid-mosaic model describes the structure of cell and organelle membranes as a mixture and movement of phospholipids, proteins, glycoproteins, and glycolipids. Cholesterol is also present in some membranes, restricting the lateral movement of other molecules in the membrane, making the membrane less fluid at high temperatures, and preventing water and dissolved ions from leaking out of the cell.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"The fluid-mosaic model explains that cell and organelle membranes are composed of a dynamic mixture of phospholipids, proteins, glycoproteins, and glycolipids. Cholesterol is also present, which regulates the fluidity of the membrane. This model emphasizes the fluid nature of the membrane, allowing for movement of molecules and proteins within it. Additionally, cholesterol helps maintain the integrity of the membrane by preventing leakage of water and ions.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275301,"front":"How do phospholipids align in a cell membrane?","back":"Phospholipids align as a bilayer in a cell membrane due to the hydrophilic heads being attracted to water and the hydrophobic tails being repelled by water.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Phospholipids align in a cell membrane as a bilayer due to the unique structure of their molecules. The hydrophilic heads, which are attracted to water, face the aqueous environment both inside and outside the cell. Meanwhile, the hydrophobic tails, which are repelled by water, are shielded from the water by facing each other in the interior of the bilayer. This arrangement allows phospholipids to form a stable barrier that separates the cell's internal environment from the external surroundings.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275302,"front":"Define peripheral and integral proteins in the context of a cell membrane.","back":"Peripheral proteins in a cell membrane do not extend completely across the membrane and provide mechanical support or connect to proteins or lipids to make glycoproteins and glycolipids. Integral proteins span across from one side of the bilayer to the other and are involved in the transport of molecules across the membrane.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Peripheral proteins in the cell membrane are located on the surface and do not span the entire membrane. They play a role in providing structural support and connecting to other proteins or lipids to form glycoproteins and glycolipids. On the other hand, integral proteins span the entire membrane and are involved in transporting molecules across the membrane. They have hydrophobic regions that interact with the hydrophobic core of the lipid bilayer.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275303,"front":"Explain the role of protein channels and carrier proteins in a cell membrane.","back":"Protein channels in a cell membrane form tubes that fill with water to enable water-soluble ions to diffuse. 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Both protein channels and carrier proteins play crucial roles in regulating the movement of substances in and out of the cell.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275304,"front":"What is a partially permeable membrane?","back":"A partially permeable membrane is the cell-surface membrane created by the arrangement of molecules within the phospholipid bilayer. It allows certain molecules or ions to pass through it by diffusion.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"A partially permeable membrane is formed by the arrangement of molecules in a phospholipid bilayer. It selectively allows certain molecules or ions to pass through by diffusion. This membrane is essential for regulating the movement of substances in and out of cells, maintaining homeostasis. It plays a crucial role in processes like osmosis and nutrient uptake.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275305,"front":"Define simple diffusion as a mode of transport in and out of cells.","back":"Simple diffusion is the net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached. It is one of the five key modes of transport in and out of cells.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Simple diffusion is a passive process that does not require energy expenditure by the cell. It occurs when molecules move freely across the cell membrane, driven by the concentration gradient. This process is important for the exchange of gases, such as oxygen and carbon dioxide, as well as small nonpolar molecules, like lipids. Simple diffusion plays a crucial role in maintaining homeostasis within cells by allowing the movement of essential molecules and waste products. It is one of the primary mechanisms by which substances enter and exit cells.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275306,"front":"Describe the process of simple diffusion.","back":"Simple diffusion is a passive process that does not require ATP. Molecules move due to their kinetic energy, allowing them to constantly move in fluids. For molecules to diffuse across the membrane, they must be lipid-soluble and small. Examples of such molecules include oxygen and carbon dioxide.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Simple diffusion is a passive process driven by the kinetic energy of molecules. It occurs in fluids and across membranes. 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It differs from simple diffusion because it involves the use of proteins to transport molecules. This is particularly important for ions and polar molecules that cannot simply diffuse across membranes. Facilitated diffusion utilizes protein channels and carrier proteins to transport these molecules across the membrane. This allows for more selective and efficient transport compared to simple diffusion.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275308,"front":"How do protein channels and carrier proteins function in facilitated diffusion?","back":"Protein channels form tubes filled with water, enabling water-soluble ions to pass through the membrane. They only open in the presence of certain ions when they bind to the protein. Carrier proteins bind with a molecule, such as glucose, causing a change in the shape of the protein. This shape change enables the molecule to be released to the other side of the membrane.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Protein channels act as tunnels that allow water-soluble ions to pass through the cell membrane. They open when specific ions bind to them. Carrier proteins, on the other hand, undergo a change in shape when they bind to a molecule like glucose. This change in shape allows the molecule to be transported across the membrane. Both protein channels and carrier proteins play crucial roles in facilitating the movement of substances across the cell membrane through facilitated diffusion.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275309,"front":"Define osmosis and explain the concept of water potential.","back":"Osmosis is the movement of water from an area of higher water potentials to an area of lower water potential across a partially permeable membrane. Water potential is the pressure created by water molecules, measured in kPa and represented with the symbol Ψ. Pure water has a water potential of zero, and when solutes are dissolved in water, the water potential becomes negative. The more negative the water potential, the more solute must be dissolved in it.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Osmosis is the passive movement of water across a semi-permeable membrane from an area of higher water potential to an area of lower water potential. Water potential is the measure of the tendency of water to move from one area to another, influenced by pressure and solute concentration. Pure water has a water potential of zero, while adding solutes decreases water potential, creating a negative value.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275310,"front":"What is an isotonic solution?","back":"An isotonic solution is when the water potential is the same in the solution and the cell within the solution.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Isotonic solutions have the same concentration of solutes as the cell, resulting in no net movement of water. This prevents the cell from shrinking or swelling, maintaining its normal state. This balance is crucial for proper cellular function and is often used in medical treatments.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275311,"front":"What does it mean when a solution is hypotonic?","back":"A solution is hypotonic when the water potential of the solution is more positive (closer to zero) than the cell.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"A hypotonic solution has a higher water potential compared to the cell. This means that there is a higher concentration of solutes inside the cell than in the surrounding solution. As a result, water will move into the cell through osmosis, causing the cell to swell or potentially burst.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275312,"front":"Define the term 'Hypertonic' in the context of cell biology.","back":"Hypertonic refers to a solution with a more negative water potential than the cell. In such a solution, both animal and plant cells will shrink and become shrivelled due to large volumes of water leaving the cell by osmosis.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Hypertonic solutions have a higher solute concentration compared to the cell. This causes water to move out of the cell through osmosis, leading to cell shrinkage and shriveling. Both animal and plant cells are affected by hypertonic solutions. The negative water potential of the solution drives the movement of water out of the cell.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275313,"front":"Describe what happens to an animal cell when placed in a hypotonic solution.","back":"When an animal cell is placed in a hypotonic solution such as pure water, a lot of water will move into the cell by osmosis. Since animal cells do not have a cell wall, the pressure will cause the cell to burst.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"When an animal cell is placed in a hypotonic solution, water molecules will move into the cell due to osmosis. This is because the concentration of solutes is higher inside the cell compared to the surrounding solution. Without a cell wall to provide structural support, the increased influx of water can cause the cell to swell and eventually burst, a process known as lysis. This is due to the osmotic pressure exerted on the cell membrane.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275314,"front":"Explain the process of active transport in cell biology.","back":"Active transport is the movement of molecules and ions from an area of lower concentration to an area of higher concentration (against the concentration gradient) using ATP and carrier proteins. The carrier proteins act as pumps to move substances across the membrane. This process is very selective, as only certain molecules can bind to the carrier proteins to be pumped.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Active transport is essential for maintaining cellular homeostasis by moving molecules against their concentration gradient. This process requires energy in the form of ATP and utilizes carrier proteins to facilitate the movement of specific substances across the cell membrane. This selective process ensures that only certain molecules are transported into or out of the cell.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275315,"front":"How does ATP and carrier proteins function in active transport?","back":"Certain molecules can bind to the receptor site on carrier proteins. ATP binds to the protein on the inside of the membrane and is hydrolysed into ADP and Pi. This causes the protein to change shape and open towards the inside of the membrane, releasing the molecule on the other side. The Pi molecule is then released from the protein, causing the protein to revert to its original shape.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"ATP and carrier proteins play a crucial role in active transport. ATP binds to the carrier protein, causing it to change shape and open towards the inside of the membrane. This allows the molecule to be transported across the membrane. The hydrolysis of ATP into ADP and Pi provides the energy needed for this process. Once the molecule is released on the other side, the Pi molecule is also released, causing the carrier protein to return to its original shape. This cycle allows for the active transport of molecules against their concentration gradient.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1275319,"front":"Describe the process of co-transport in the context of sodium and glucose ions absorption.","back":"In co-transport, sodium ions are transported by active transport from the epithelial cells to the blood via a protein carrier. This lowers the concentration of sodium in the epithelial cell, creating a concentration gradient between the ileum and the epithelial cell.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Co-transport involves the movement of sodium ions and glucose molecules across the epithelial cells. Sodium ions are actively transported out of the epithelial cells into the blood, creating a lower concentration of sodium inside the cell. This concentration gradient allows sodium ions to passively diffuse back into the cell, along with glucose molecules, through a protein carrier. This process allows for the absorption of both sodium and glucose from the ileum into the epithelial cells.","deleted_at":null,"flashcard_deck_id":"6omPP","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}}]

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