2.4 - Movement of Substances Flashcards
What substance move into cells?
- Oxygen
- Water
- Glucose
- Protein
- Carbon dioxide (in plant cells)
- Amino acids
- Hormones
- Salt (ions)
What substances move out of cells?
- Carbon dioxide (particularly in animals)
- Waste (urea)
What are the cell inputs for Autotrophs?
- Photo-autotrophs require light for photosynthesis to occur, along with the carbon dioxide and water needed to produce organic molecules for an energy source
- Plants require a range of inorganic nutrients, such as nitrogen, phosphorous and magnesium to build important molecules in their cells
E.G.: magnesium is vital molecule in chlorophyll
What are the cell inputs for Heterotrophs?
- Heterotrophic cells cannot photosynthesise and therefore must be supplied with a source of energy through their food
A typical diet of a heterotroph will contain proteins, carbohydrates, lipids and nucleic acids, as well as water, mineral nutrients (eg: calcium and iron) and vitamins (eg: vitamin C)
What are the products which are removed during waste removal in the cell?
- As well as useful products, most metabolic activity in cells produces waste products which can be toxic if they accumulate (eg: CO2 and Urea)
- Numerous waste products are produced in plants and animals that need to be removed to maintain a stable intracellular environment
- This enabled metabolic processes to occur efficiently without disruption
- For products to enter or leave cells, they must cross the cell membrane, which is where membrane transport processes become important
How is CO2 removed from the cell?
CO2 is produced during aerobic respiration and as soon as it is produced it is transported out of cells and into the blood stream of animals to be removed via the lungs
- In plants it can be used in photosynthesis, but if the rate of aerobic respiration is greater than the rate of photosynthesis (eg: at night) then the carbon dioxide will be excreted from the leaves
How is Urea removed from the cell?
- Urea is another metabolic waste produced in animals and is created by a biochemical process in the liver
- It moves out of the liver into the bloodstream where it is removed by the kidneys to be excreted in urine.
What are different properties affect the rate of movement of substances across the cell membrane?
- Surface area to volume ratio of the cell
- Concentration gradients
- The physical and chemical nature of the substances being transported
- Concentration gradients
How does surface area to volume ratio affect the rate of movement of substances?
- As the size of the cell increases, the surface area to volume ratio decreases (for a given shape)
- Result = a decrease in efficiency of exchange of materials with the surroundings
○ Most cells are very small because this allows them to get their requirements and excrete waste products more easily by diffusion
○ Reduction in SA:Vol in growing cells is thought to be a stimulus for cell division
○ Significance for cells: - The cell surface is the site of exchange of materials between the cell and it’s surroundings
- Result = a decrease in efficiency of exchange of materials with the surroundings
What is surface area to volume ratio?
- The ratio is a numerical value that represents the relationship between the external surface and its internal volume.
Some cells have an increased surface area due to their shape. What are these cells?
○ Red blood cells
○ Intestinal epithelial cells
- Thin
- Long
- FlatWhat is Diffusion?
- Molecules in cells are not stationary, but move constantly in a random manner.
- The molecules in gases and liquids move so that the net effect is to move from regions of high concentrations to regions of low concentration - this is called diffusion.
- Diffusion moves down the concentration gradient. from high to low.
- The process is passive as it does not require energy.
- As the membrane is made of hydrophobic lipids, only small non-polar molecules (eg: oxygen) can easily diffuse across it
What is the Concentration Gradient?
○ The difference in concentration of the substance in two regions is called the concentration gradient
- The greater the difference in concentration, the steeper the gradient
- The steeper the gradient, the more rapidly diffusion will occur
What is Facilitated Diffusion?
- As large and/or polar molecules have difficulty diffusing across the cell membrane, help is required for them to move
- Two types of special proteins in the cell membrane allow these molecules to move along their concentration gradients
- They are channel proteins and carrier proteins
What are Channel Proteins?
- Channel proteins provide a pore in the membrane for hydrophilic molecules such as glucose to move through.
- do not require an input of energy to work, as the molecules move along their concentration gradient still
