Shaina Cailles
- In the life cycles of a fern and a flowering plant, compare and contrast each of the following:
- The gametophyte generation.
- Both produce gametes that are haploid. In flowering plants, male and female gametophytes are produced in the sporophyte, and are dependent on it for nutrition. The male gametes are pollen grains, the females embryo sacs. Each gametophyte develops from a different type of spore. In ferns, the archegonia produce eggs and antheridia produce sperm. The archegonia and antheridia are on the prothallus, which is a heart shaped structure. Archegonia has a neck and the venter, which contains the egg. The antheridia has a wall of cells protecting the gametes. The gametes don’t depend on the prothallus, they are photosynthetic and have rhizoids for anchoring and water absorption.
- Sperm transport and fertilization
- In ferns, the transportation of sperm to the eggs for fertilization needs a moist environment (for mobility). The cells of the neck canal and ventral canal disappear and releases a chemical that attracts the sperm. Fertilization takes place in the venter of the archegonium.
- In flowering plants, pollen (the male gametes) travels from the anther to the stigma of the pistil. A pollination agent is needed, such as a bee or a butterfly, needs to pollinate the egg. The pollen grain then germinates and grows through the style. Double fertilizations (2 sperm, 1 embryo sac) happen after the pollen tube goes through the ovules.
- Embryo protection
- In ferns, since the embryo is in the archegonium during fertilization, it depends on it for protection as well. It is dependent on the gametophyte for nutrition in the early stages.
- In flowering plants the embryo’s are protected by seeds, much like a chicken’s egg. The outer layer is hard, and makes up the ovule. When enclosed in a fruit, the fruit comes from the ovary wall. The ovary wall has three layers, endocarp, mesocarp, and exocarp, together forming the pericarp. For nutrition, the embryo depends on the endosperm.
- Relate the structure of an angiosperm leaf to each of the following:
- Adaptations for photosynthesis and food storage
- The cuticles on the outermost layer are clear, so it can let light go through. Also regarding the leaf, it is shaped in a way to absorb more sunlight and be more efficient. The palisade parenchyma and spongy parenchyma are where the photosynthesis takes place. For food, the stoma controls the passage of gas and water.
- Adaptations for food translocation and water transport.
- The xylem help transport food and water. The xylem transports water to the leaf tissue and the phloem transports nutrients from the leaf tissue to the rest of the plant. This happens with bulk flow, powered by turgor pressure, and the nutrients move from the leaves to the sinks. Water is lost by transpiration, when it evaporates from the plants, usually happening when the stoma are open during photosynthesis. Desert plants also have C4, which is more efficient than the normal C3.
- Specialized adaptations to a desert environment.
- Because deserts usually have much more sun than the rest of the earth, smaller leaves are needed to take in enough sunlight. Since water is lost when the stoma are open, desert plants can have less stomata or have them open only at night. Desert plants also have C4, which is more efficient than the normal C3.
- Define the following plant responses and explain the mechanism of control for each. Cite experimental evidence as part of your discussion.
- Phototropism- The characteristic of growing in the same direction of the light source. Found in plants and sometimes other organisms like fungi. Charles Darwin and his son Francis did studies on phototropism. They found that the plants would only grow towards the light if the coleoptile, a section of the stem near the base, was exposed to the light. Later, Peter Boysen-Jensen found that a chemical signal from the coleoptile to the tip. They found that the growth was from below the tip of the coleoptile. when a gelatin block separated the tip, the plant continued to grow, but it didn’t with a mica.
- Photoperiodism- The physiological reaction of organisms to the length of day or night, found in plants and animals. Short day plants need a shorter day to flower, where long day plants flower when there are longer days, such as late spring and summer. Day neutral plants are not affected by the length of day and flower according to the plants maturity. It is very important to know that these plants (not day neutral) are actually controlled by night, and not day. If the night phase is disturbed, for example the cocklebur, will not flower. Plants are most sensitive to red light, and if exposure is over by even one minute flowering can be stopped. Florigen is the hormone associated with photoperiodism, found in leaves. It has not been formally identified though.
- Describe the structure of a bean seed and discuss its germination to the seedling stage. Include in your essay hormonal controls, structural changes, and tissue differentiation.
- Structure
- The embryo is covered by the seed coat for protection. The hypocotyl, a stem, ends in the radicle, or embryonic root. This is where it is attached to the epicotyl at the end. The radicle is usually at the bottom of the bean structure.
- Germination
- inbibition- the uptake of water due to the low water potential of the dry seed. The imbibation causes the seed coat to break. The radicle is the first to come out of the coat, then the coleoptile, foliage leaves. For this to happen oxygen and correct temperature is needed. Hormonal controls include the increase of auxin, gibberellins to stimulate growth, cytokinins for cell division, and absesic acid to slow root growth.
- Describe the effects of plant hormones on plant growth and development. Design an experiment to demonstrate the effect of one of these plant hormones on plant growth and development.
- Auxin stimulates stem elongation, root growth, cell differentiation, enhances apical dominance, promotes xylem differentiation, retards leaf abscission. Cytokinins affect root growth and differentiation, stimulate cell and division. Gibberellins promote seed and bud germination, stem elongation, and leaf growth. Brassinosteroids inhibit root growth, retard leaf abscission, promote xylem differentiation. Ethylene promotes fruit ripening, opposes some auxin effects.
- Experiment: Give plants a variety of amounts of auxin and see the effects.
- Trace the pathway in a flowering plant as the water moves from the soil through the tissues of the root, stem, and leaves to the atmosphere. Explain the mechanisms involved in conducting water through these tissues.
- Soil particle to root hair to xylem to stomata to mesophyll cells to stoma to atmosphere.
- Mechanisms.
- Osmosis- diffusion of water through semipermeable membranes
- Transpiration- evaporation of water from leaf
- Cohesion- Water molecules stick together
- Adhesion- Water molecules stick to, not attract
- Root pressure- force made by root on water column
- Water potential- Negative pressure in leaves, positive in roots
- Discuss the adaptations that have enabled flowering plants to overcome the following problems associated with life on land.
- The absence of an aquatic environment for reproduction.
- Pollination. Flowers are developed in order to reproduce, flowers help by attracting animals to pollinate (pollination aids). Pollen for males, seed for females. The seeds are coated with a hard outer layer to protect it. Fruits are made so animals can it them and the seeds will spread by the means of their feces. Seeds can be dormant for a long time.
- The absence of an aquatic environment to support the plant body.
- Roots to help hold to the ground, stems for support, vascular tissue to help hold shape, cell walls more rigid, turgor pressure.
- Dehydration of the plant.
- The cuticle was developed, a waxy outer layer found in the leaves to prevent water from leaving the plant. Stomates control water movement, in trees scales and cork help keep water in. Xylem transports water.
- Describe how the following adaptations have increased the evolutionary success of the organisms that posses them. Include your discussion the structure and function related to each adaptation.
- C4 metabolism- Plants with the C4 metabolism are more efficient because they do not waste oxygen during photorespiration, the enzyme RuBisCO is prone to. It gets more ATP than the usual C3 metabolism.
- Pollen- Pollen is an adaptation of plants to fit living in a land environment as opposed to an aquatic one. Microsporangia contain diploid microsporocytes that divide by meiosis to produce haploid microspores, each of which develops into a pollen grain. The pollen grains mature into a gametophyte and divides the nucleus into two sperm. After this, the pollen grains must land on a stigma of a carpel of a plant and the pollen tube begins to grow.
- Seeds- An embryo, with a food supply covered in a protective coat from the integument. This is another adaptation of plants to survive living on land. It is possible for the seeds to survive harsh environments and disperse more widely. They can stay dormant for years after being released from the parent plant. See #1.
- Angiosperms and vertebrates obtain nutrients from their environment in different ways.
- Discuss the type of nutrition and the nutritional requirements of angiosperms and vertebrates.
- Angiosperms are autotrophs. They make their own food using energy from the sun and other nutrients from the soil. Nutrients needed in both angiosperms and vertebrates are nitrogen, phosphorous, potassium, and calcium. Vertebrates get their energy from other sources, such as plants and other animals.
- Describe 2 structural adaptations in angiosperms for obtaining nutrients from the environment. Relate structure to function.
- Roots are an adaptation. They allow nutrients to be taken from a greater space, and with root hairs increase overall root surface. Photosynthesis is another adaptation. They take energy from the sun and convert it to glucose and ATP. Chlorophyll is in the leaves, that are designed to help take in as much sun as needed.
- Interdependence in nature is evident in symbiosis. Explain two symbiotic relationships that aid in nutrient uptake, using examples from angiosperms and/or vertebrates.
