[14052014] Virtual Lab: Plant Transpiration ≡
Posted on Wednesday, May 14, 2014 at 11:42 PM
The following content is a response to this virtual lab.- Describe the process of transpiration in vascular plants:
- Investigate the effect of various environmental factors on the transpiration rate of plants
[08052014] Plant Hormones ≡
Posted on at 10:47 PM
Auxins: Auxin, or IAA (indoleacetic acid), promotes plant growth by facilitating the elongation of developing cells. Auxin does this by increasing the concentration of H+ in primary cell walls, which, in turn, activates enzymes that loosen cellulose fibers. The result is an increase in cell wall plasticity. In response, turgor pressure causes the cell wall to expand, thus generating growth. Auxin is produced at the tips of shoots and roots, where, in concert with other hormones, it influences plant responses to light (phototropism) and gravity (geotropism). In addition, auxin is active in leaves, fruits, and germinating seeds. Structurally, auxin is a modified tryptophan amino acid. After synthesis from tryptophan, it is actively transported (using ATP) from cell to cell in a specific direction (polar transport), by means of a chemiosmotic process.
Auxin and Phototropism:
- Auxin is produced in the apical meristem, moves downward by active transport into the zone of elongation, and generates growth by stimulating elongation.
- When all sides of the apical meristem are equally illuminated, growth of the stem is uniform and the stem grows straight.
- When the stem is unequally illuminated, auxin moves downward into the zone of elongation but concentrates on the shady side of the stem. Auxin that would have normally accumulated on the sunny side ends up on the shady side.
- The higher concentration of auxin in the shady side of the stem causes differential growth; that is, since auxin generates growth by stimulating elongation, the shady side grows more than the sunny side. When the shady side grows more than the sunny side, the stem bends toward the light.
- Gravitropism (or geotropism), the response to gravity by stems and roots, is not well understood. In general, both auxin and gibberellins are involved, but their action depends on their relative concentrations and the target organ (root or stem). The role of auxin appears to agree with the following:
- If a stem is horizontal, auxin produced at the apical meristem moves down the stem and concentrates on its lower side. Since auxin stimulates cell elongation, growth of the lower side is greater than that of the upper side, and the stem bends upward as it grows.
- If a root is horizontal, auxin is produced at the apical meristem (root tip), moves up the roots, and, as in stems, concentrates on the lower side of the root. However, in roots, auxin inhibits growth. This is because concentrations of auxin are higher in roots than in stems.
Abscisic Acid: Abscisic acid (ABA) is a growth inhibitor. In buds, it delays growth and causes the formation of scales in preparation for overwintering. In many species of plants, ABA maintains dormancy in seeds. Dormancy in these seeds is broken by an increase in gibberellins or by other mechanisms that respond to environmental cues such as temperature or light. In some desert species, seed dormancy is overcome by the leaching of ABA from seeds by rains. Although ABA is named for the process of abscission, its influence on the abscission of leaves, flowers, and fruits is controversial.
Ethylene: Ethylene is a gas that promotes the ripening of fruit. During the later stages of fruit development, ethylene gas fills the intercellular air spaces within the fruit and stimulates its ripening by enzymatic breakdown of cell walls. Ethylene is also involved in stimulating the production of flowers. In addition, ethylene (in combination with auxin) inhibits the elongation of roots, stems, and leaves and influences leaf abscission, the aging and dropping of leaves.
[02052014] Flora ≡
Posted on at 10:46 PM
Fig1: Photograph and Sketch of two flowers (taken by Rachel Utomo)
Fig1: Photograph and Sketch of lavenders (taken by Rachel Utomo)
Sexual Reproduction In Flowering Plants
The organs of a plant that are involved in its sexual reproduction are its flowers. Figure 3 shows the structure of a typical flower
Fig3: An insect pollinated Flower
The male gametes are produced inside the anthers. The female gametes are produced inside the ovules. As in human, the gametes are made by meiosis. However, unlike humans, many flowers produce both males and female gametes. They are said to be hermaphrodite. (There are some hermaphrodite animals. Earthworms and snails are hermaphrodites).
Pollination
Sexual reproduction depends on a male gamete fusing with a female gamete. In flowers, the male gametes are inside the pollen grains in the anthers, while the female gametes are in the ovules in the ovary.
The journey of a male gamete to a female gamete in a flower takes place in two stages. First, the male gametes are carried inside the pollen grains, to a stigma. Second, the pollen grain grows a tube from the stigma to the ovule, through which the male gamete can safely travel to the female gamete.
The first stage of this journey, in which pollen grains are transferred from anther to stigma, is called pollination. We can define pollination as the transfer of pollen grains from the male part of a flower (anther or stamen) to the female part of a flower (stigma).
Insect and Wind Pollination
Insects come to the flower to collect nectar or pollen for food. The coloured petals, and perhaps a scent, advertise the presece of this food and therefore attract insects to the flower.
As the insects push down towards the nectaries, they brush past the anthers. Pollen grains stick to their bodies. When the insects feed at a second flower, some of the pollen grains may be brushed onto the stigma.
Some flowers fo not use insects for pollination, however. They rely on the wind. These flowers do not need to produce nectar, nor do they need brightly coloured petals. Wind-pollinated flowers are usually dull green or brown. Their anthers and stigmas hang outside the flower, to catch the wind. They often produce larger amounts of pollen than insect-pollinated flowers, to allow for the wastage that occurs. The wind, unlike an insect, will not carry the pollen directly to another flower. Pollen grains from wind-pollinated flowers tend to be very smooth and light, whereas insect-pollinated flowers often produce pollen with spikes that can stick onto an insect's body.
Self-Pollination and Cross Pollination
Pollen can be carried from an anther to a stigma on the same plant. This is called self-pollination. It cane ven be carried to the stigma on the same flower.
Alternatively, pollen can be carried from an anther to a stigma on a different plant of the same species. This is called cross-pollination.
Both self-pollination and cross-pollination are part of sexual reproducton. Both of them involve gametes (insde the pollen grain and inside the ovules) and fertilisation. Even self-pollination is apart of sexual reproduction, even though the male and female gametes come from just one individual.
Fertilization
Once it has arrived on a stigma, a pollen grain will begin to grow a tube. It is stimulated to do this by chemicals, usually including sugars, secreted by the stigma, Different species of flowers secrete slightly different combinations of chemicals, so pollen grains will normally only grow tubes if they land on a stigma of their own species.
The pollen tube grows right down through the style, towards and ovule inside the ovary. Enzymes are secreted from the tip of the pollen tube and these enzymes digest the tissues of the style. Inside the tube, the male gamete travels to the ovule. The male gamete is not a complete cell like a sperm cell; it is simply a haploid nucleus
[02052014] Botany Of Desires: The Human Bumblebee ≡
Posted on Thursday, May 1, 2014 at 11:31 PM
As a response to this excerpt , I have created a pinterest board on some of the things it taught me, as well as other things I recalled as I read the passage.[23042014] Predator Versus Prey Simulation: Wolves & Rabbits ≡
Posted on Thursday, April 24, 2014 at 11:21 PM
Note: The green cells represent the population in a new generation/ round
Correction: The cell immediately below the seventh generation should have said "4" instead of "3."
Analysis:
For this simulation, we were unable to complete more than 9 generations of observation, meaning that the graph above appear incomplete. However, to compensate for an incomplete graph, I will post a predator-vs-prey simulation graph completed from another source in addition to a general analysis of the graph.
In the line graph above, both the total population of rabbits and the wolves increase. The rabbits' population doubles every generation, whereas the wolf's population can only be doubled for every three rabbits it catches. This is the reason why the wolf has a slower population growth rate in comparison to the rabbits.
When looking at the graph, the number of arctic rabbits (white in colour) surpass that of a rabbit of other colours. This is because we have to take in setting to consideration, which in this case is the arctic, where snow is ubiquitous. With this piece of valuable information, it isn't hard to discern that arctic rabbits have the advantage of camouflage. Other species of rabbits like the "honeydew green" rabbit and the "olive green" rabbit are the first to become extinct because of the stark contrast between their fur and surroundings. The "green" rabbits do end up surviving for the nine generations recorded, but do so in smaller numbers in comparison to the arctic rabbit.
Above is a general graph that compares the population of prey and predators. Like I mentioned above, I have posted this general graph as to compensate for the lack of data recorded for this simulation due to lack of time. Although this graph is not highly detailed, it does serve the purpose of explaining the relationship between prey and predators. As you can see, the number of prey increases as the number of predators decrease, and the number of prey decrease when the number of predators increase.
When the number of predators increase, it will need prey to sustain the population. Consequently, the need for more food resources end up depleting the prey population because the prey population is the food resource for the predators. As a result of having the prey population decrease faster than the rate of prey reproduction, the population of prey will naturally decrease.
As the prey population decreases, the predators source of food also decreases, meaning that its population will need to compete for nutritional resources. As a result, only a fraction of the population deemed "fit" will be able to retrieve this source of food and survive, while the rest of the population steadily depletes. However, when the graph breaks even after the predator population decreases, the cycle begins again with a larger population of preys than predators. This is because there are less predators to hunt for prey, meaning that prey can finally reproduce and repopulate their species. The cycle then repeats again.
Predators and prey co-evolve together. This co-evolution can be accredited to the fact that mutations may form traits favourable for some organisms in the survival-of-the-fittest competition. For example, mutations may make the arctic rabbit run faster, increasing their probability of escape from the wolf. Other arctic rabbits without this mutation will inevitably be consumed by the wolf, and the ones with the mutation are left to breed, creating a new generation of faster arctic rabbits. Similarly, the wolves that are unable to successfully capture any food will eventually die, leaving the wolves, who are faster, more discreet , and able to catch and consume these quicker rabbits, to breed. As a result, the genetic mutation that makes these wolves faster are passed on, and the difference in speed between the rabbit and the wolf will return to more or less the same as it was previously. Theoretically, this means that wolves and rabbits can only get faster after every generation.
Also, this is all I could think about every time I wrote "wolf." Sorry. 엑소 진짜 대박.
About Me
Rachel Putri Utomo
Block F, Honors Biology
Mr. Kevin Quick
Academic Year 2013-2014