Chapter 4 Flashcards
How do salty soils affect the matric potential and, in turn, affect root pressure and overall water uptake?
Plants growing in places with strong matrix potentials typically have additional adaptations to help them extract water. Plants living in deserts, for example, can extract water that is tightly held by soil particles. Plants living in salty soils can also meet the challenge of extracting water. In both situations, plants have evolved to increase the concentrations of amino acids, carbohydrates, or organic acids in their root cells to create higher osmotic forces that help move water into the roots. Maintaining these higher concentrations of organic compounds, however, comes at a high metabolic price because the plant must divert some of its energy that would normally be used for growth and instead use it to manufacture these compounds.
Based on your knowledge of the relationship between volume and surface area, why do clay soils hold more water than sandy soils?
Clay has a smaller particle than sand. For a given volume of soil, smaller particles have a larger total surface area than larger particles. Therefore, soils with a high proportion of clay particles hold more water on their surfaces, Soils with a high proportion of sand particles tend to dry out because water quickly drains away, leaving many tiny pockets of air between the large sand particles. Although clay soils retain a lot of water, clay particles can hold water molecules so tightly that it can be difficult for plants to extract the water from the soil.
If you were breeding cotton plants to have increased water uptake in dry soils, you could breed plants that contain more amino acids and carbohydrates in the root cells. Why would this be effective, and why might crop yield be negatively affected?
Increasing the conc of amino acid and carb creates higher osmotic forces to let more water into the roots and more carbs more energy used
How do CAM plants solve the problem of obtaining for photosynthesis while minimizing water loss?
CAM plants open their stomata for gas exchange during the cool night, when transpiration is minimal, and then conduct photosynthesis during the hot day. Because CAM plants can conduct gas exchange during the night when the air is cooler and more humid, a plant using CAM photosynthesis reduces its water loss. Thus, CAM photosynthesis is an adaptation that results in extremely high water-use efficiencies and enables plants that use this pathway to live in very hot and dry regions of the world. C4 plants do this ex. cactus
How might the fitness cost of photorespiration in plants favor the evolution of plants?
The problem of photorespiration is caused, in part, by closed stomata. This leads to high concentrations and low CO2 concentrations in the leaves. One potential solution is to keep the leaf stomata open. This would permit free gas exchange, allowing CO2 to enter the leaves and to exit the leaves. This strategy works as long as plants can replace the water they also lose by transpiration when the stomata are open. However, this solution may be too costly in hot, dry environments where water is scarce. When such costs are too high, natural selection will favor traits that can either reduce the demand for water or reduce the loss of water.
How do leaf hairs that surround guard cells reduce water loss through the process of forming a boundary layer?
Leaf hairs reduce water loss by forming a boundary layer. For water loss to happen (transpiration) the water vapor has to diffuse thru the boundary layer. The more leaf hairs that surround the guard cells the larger the boundary layer will be and the harder it becomes for water vapors to diffuse.
when animals hibernate, they lower their temperature. How would this reduce the rate of heat lost through conduction?
The rate of heat lost is higher when there is a bigger difference in temp between the animal and the environment. So if the hibernating bear lowers its internal temp it decreases its heat lost to the environment. Heat travels from warmer to cooler, so if bear is cooler not as much heat will travel out.
In addition to having highly efficient kidneys, what behaviors could you imagine desert animals using to reduce water loss?
They might hunt when it’s colder outside at night to limit water lost. Ex. The kangaroo rat conserves water by hunting for food during the night and staying in a cool and humid underground burrow during the hot days. They also have highly efficient kidneys that can recover more water from urine prior to excretion.
If you designed an experiment to determine how temperature and the species composition of seeds affect the growth and reproduction of seed-eating birds, what would be the independent and dependent variables?
Dependent variables: Growth and reproduction of seed-eating birds
Independent variables: Temperature and species composition of seeds
compare and contrast the adaptations that have evolved in aquatic and terrestrial environments.
common: get most offspring to spread genes
contrast: swimming faster, running faster etc.
