How does coupled transport allow a molecule to be transported
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Cell membranes surround each cell and some organelles, such as the nucleus and the Golgi body. They are comprised of a phospholipid bilayer and this acts as a semipermeable barrier that regulates what enters and exits the cell or organelle. This is highly important as this is how cells can obtain molecules such as oxygen and remove waste products like urea. Show
There are two main ways in which molecules are transported across the cell membrane:
The main difference between these modes of transport is that active transport requires energy in the form of ATP, but passive transport does not. What are the passive transport methods?Passive transport refers to transport across the cell membrane that does not require energy from metabolic processes. Instead, this form of transport relies on the natural kinetic energy of molecules and their random movement . There are three modes of passive transport:
Simple diffusionSimple diffusion is the movement of molecules from a region of high concentration to a region of low concentration until an equilibrium is reached. Oxygen can freely diffuse through the cell membrane using this form of passive transport. Simple diffusion Facilitated diffusionFacilitated diffusion is the same as simple diffusion but this form of transport uses membrane proteins, such as channel proteins and carrier proteins. Channel proteins provide a hydrophilic channel for the passage of charged and polar molecules, like ions. Meanwhile, carrier proteins change their conformational shape for the transport of molecules. Glucose is an example of a molecule that is transported across the cell membrane through facilitated diffusion. OsmosisOsmosis is the movement of water molecules from a region of high water potential to a region of lower water potential through a semipermeable membrane. This form of transport looks very different between plant and animal cells as plant cells have cell walls surrounding each cell. Cell walls allow plant cells to withstand water flowing in. However, animal cells are more prone to cell bursting as they do not have this added support. The rate of osmosis can be increased if aquaporins are present in the cell membrane. Aquaporins are membrane proteins that selectively transport water molecules. The uptake of water by plant root hair cells is dependent on this form of passive transport. The diagram shows the movement of molecules through the cell membrane during osmosis What are the active transport methods?Active transport is the transport of molecules across the cell membrane using carrier proteins and energy from metabolic processes in the form of ATP. Carrier proteins are membrane proteins that allow the passage of specific molecules across the cell membrane. They are used in both facilitated diffusion and active transport. Carrier proteins use ATP to change their conformational shape in active transport, allowing a bound molecule to pass through the membrane. In facilitated diffusion, however, ATP is not needed to change the shape of the carrier protein. Transport Across Cell Membrane - Key takeaways
Frequently Asked Questions about Transport Across Cell MembraneThere are two ways in which molecules are transported across the cell membrane: passive transport and active transport. The passive transport methods are simple diffusion, facilitated diffusion osmosis - these rely on the natural kinetic energy of molecules. Active transport requires energy in the form of ATP. Amino acids are transported across the cell membrane via facilitated diffusion. Facilitated diffusion uses membrane proteins to transport molecules. Amino acids are charged molecules and therefore need membrane proteins, specifically channel proteins, to cross the cell membrane. Membrane proteins such as channel proteins and carrier proteins facilitate transport across membranes. This type of transport is called facilitated diffusion. Water molecules are transported across the cell membrane via osmosis which is defined as the movement of water from a region of high water potential to a region of lower water potential through a semipermeable membrane. The rate of osmosis is increased if aquaporins are present in the cell membrane. Final Transport Across Cell Membrane Quiz
Question What form of transport relies on the natural kinetic energy of molecules? Show answer Answer Passive transport. This includes simple diffusion, facilitated diffusion and
osmosis. Show question
Question What form of transport requires carrier proteins and energy in the form of ATP? Show answer
Answer Simple diffusion is the movement of molecules from a region of high concentration to a region of low concentration. Show question
Question What is the difference between simple diffusion and facilitated diffusion? Show answer Answer Facilitated diffusion requires membrane proteins, such as channel proteins and carrier proteins.
Simple diffusion does not require membrane proteins. Show question
Question Osmosis is the movement of water molecules from a region of high water potential to a region of low water potential, through a __________ ________. Show answer
Question What can increase the rate of osmosis? Show answer Answer If aquaporins are present in the cell membrane. Show question
Question What form of transport does the uptake of mineral ions through the plant root hair cell rely on? Show answer
Question What form of transport does the uptake of glucose molecules rely on? Show answer
Question What form of transport does the uptake of oxygen rely on? Show answer
Question Identify 2 types of active transport methods. Show answer Answer Cotransport and bulk transport. Show question
Question Where can you find cell membranes? Show answer Answer Cell surface membranes surround each cell. Membranes also surround some organelles, such as the nucleus. Show question
Question How do cell membranes allow cell communication? Show answer Answer Glycolipids and glycoproteins act as receptors and antigens. Signaling molecules can bind to these receptors and
antigens. This will elicit chemical reactions within the cell. Show question
Question What is compartmentalisation and why is it important? Show answer Answer Compartmentalization is the separation of each cell and each organelle so that incompatible metabolic reactions are kept separate. This
is important so that the optimal conditions for each metabolic reaction are maintained without interfering with other reactions. Show question
Question What kind of molecules are cell membranes highly permeable to? Show answer Answer Small, uncharged polar molecules. Show question
Question What kind of molecules are cell membranes impermeable to? Show answer Answer Large, charged nonpolar molecules. Show question
Question What is the model that is widely used to describe the cell membrane structure? Show answer
Question What are the two distinct regions of a phospholipid? Describe the phospholipid bilayer. Show answer Answer The hydrophilic phospholipid heads face the aqueous environment (extracellular and intracellular) while the hydrophobic phospholipid tails form a core away from the aqueous environment. Show question
Question Phospholipid fatty acid tails that have kinks are ________. This is because they have at least one carbon _____ ____. Show answer Answer Unsaturated. Double
bond. Show question
Question What are the two types of membrane protein? Show answer Answer Integral proteins and peripheral proteins. Show question
Question What are the two types of integral protein and what is their main function? Show answer Answer Channel proteins and carrier proteins. Their main function is to transport molecules
across the cell membrane. Show question
Question What are the main functions of glycoproteins? Show answer Answer Cell adhesion and cell communication. Show question
Question What are the main functions of glycolipids? Show answer Answer Cell adhesion and cell recognition. Show question
Question What are the 2 main functions of cholesterol? Show answer Answer Preventing water and ions from leaking out of the cell and regulating membrane fluidity. Show question
Question At colder temperatures, cholesterol will prevent the _________ of phospholipids. Show answer
Question What happens to cell membranes when placed in a solvent that is less polar than water, such as ethanol? Show answer Answer The cell membrane structure breaks down and is dissolved.
The cell membrane becomes highly permeable and the cell contents leak out. Show question
Question Why do cell membranes become more permeable at higher temperatures? Show answer Answer At higher temperatures, phospholipids have more kinetic energy and move more. This enables
small molecules to pass through the cell membrane. Show question
Question What is the pigment that is responsible for the color of beetroot? Show answer
Question When investigating how temperature affects cell membrane permeability in beetroot cells, what does a higher absorbance reading indicate? Show answer Answer A higher absorbance reading indicates
there is more pigment present in the sample solution. This means that the cell membrane structure is more permeable than the betalain pigment has leaked out of the cell and into the solution. Show question
Question What process does the gaseous exchange of oxygen and carbon dioxide rely on? Show answer
Question What is the waste product of the breakdown of amino acids? How does it enter the blood? Show answer Answer Urea. There is a higher concentration of urea in liver cells
than in the blood. This concentration gradient means urea diffuses into the blood via simple diffusion. Show question
Question Define facilitated diffusion. Show answer Answer The movement of molecules down their concentration gradient, using membrane proteins. Show question
Question What are channel proteins? Show answer Answer Transmembrane proteins which provide a hydrophilic channel for the passage of charged molecules, like ions. Show question
Question What are the different types of stimuli that trigger the opening or closing of channel proteins? Show answer Answer Voltage, mechanical pressure and ligand binding. Show question
Question What are carrier proteins? Show answer Answer Transmembrane proteins which undergo a reversible conformational change for the passage of molecules. Show question
Question What processes require the presence of carrier proteins? Show answer Answer Both passive and active transport across the cell membrane. Show question
Question What kind of process allows the nerve impulse to travel along axons? Identify a protein that is required for this process. Show answer Answer Facilitated diffusion.
Voltage-gated sodium ion channels are needed for the passage of ions. Show question
Question Describe the molecular properties of glucose and what it means for its transport across cell membranes. Show answer Answer Glucose is a large and highly polar molecule. This means it needs
membrane proteins for its transport across cell membranes. Show question
Question Identify the membrane protein needed in glucose transport. Show answer Answer Glucose transporter proteins (GLUTs). Show question
Question What are the main factors that affect the rate of diffusion? Show answer Answer Concentration gradient, distance, temperature, surface area and molecular properties. Show question
Question How is a steep concentration gradient maintained for gaseous exchange? Show answer Answer Continuous ventilation and blood flow maintain the steep concentration gradient. Show question
Question Describe the diffusion distance in gaseous exchange? Show answer Answer The diffusion distance is kept very small. The capillary endothelium and alveoli walls are only one cell thick. The capillaries are so wrapped tightly around the alveoli. Show question
Question How is a large surface area provided for in gaseous exchange? Show answer Answer Many alveoli are present in each lung. Show question
Question When the membrane potential of neurones become less negative, what process occurs? Show answer
Question Define osmosis in terms of water potential. Show answer Answer Osmosis is the movement of water molecules down a water potential gradient, through a semipermeable membrane. Show question
Question What is the water potential of pure water? Show answer
Question Water molecules will move from a more dilute solution to a more ______ solution. Show answer
Question Describe the water potential of a solution as more solutes are dissolved in it. Show answer Answer The water potential becomes more negative as more solutes are dissolved in a
solution. Show question
Question What kind of membrane is needed for osmosis? Show answer Answer A semipermeable membrane. Show question
Question What are the three types of tonicity? Show answer Answer Hypotonic, isotonic and hypertonic. Show question
Question Compare plant cells placed in a hypertonic solution to plant cells placed in a hypotonic solution. Show answer Answer In a hypertonic solution, plant cells will undergo plasmolysis and will become flaccid. But in a hypotonic solution, planning cells will become turgid and firm. Show question How does coupled transport work?Coupled transport is defined as the simultaneous transport of two substances across a biological membrane. It may be a symport or antiport depending on the direction of movement of the two substances. If both move in the same direction it is a symport type of coupled transport.
How does co transport or coupled transport work?Antiporters use the mechanism of cotransport (coupling the movement of one ion or molecule down its concentration gradient with the transport of another ion or molecule up its concentration gradient), to move the ions and molecule in opposite directions.
How do molecules get transported?Carrier proteins bind specific molecules to be transported on one side of the membrane. They then undergo conformational changes that allow the molecule to pass through the membrane and be released on the other side.
Does coupled transport use ATP?In secondary active transport, also known as cotransport or coupled transport, energy is used to transport molecules across a membrane; however, in contrast to primary active transport, there is no direct coupling of ATP.
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