Selasa, 12 April 2011

Plant Physiology "introduction"

Name : Andi Citra Pratiwi

Reg. No : 091404170

  1. Compare and contrast autotrophs and heterotrophs!

Answer: Autotrophs are the organisms which are able to manufacture their own foods, since they are able to make organic compounds from inorganic materials in the environment by using light energy (as energy source) and chlorophyll through photosynthesis process. Plant is an autothroph organism. Meanwhile, heterotrophs are the organisms which are not able to manufacture their own foods, since they can not make organic compounds from inorganic compounds. Thus, they must obtain their food (organic compounds) from the environment. Examples of heterotrophs are carnivores, herbivores, and decomposers.

Noteworthy, autotrophic nutrition lays down the building blocks of life and provides complex organic molecules for the consumption of heterotrophic organisms. Without autotrophic nutrition, there would be no life.

  1. Discuss the consequences of being autotrophic. How have plants responded to life as autotrophs?

Answer: Plants require specialized structures for adapting the autotrophic mode of nutrition. Autotroph means that the plant should process the inorganic molecules to be organic molecules. Since the plants can not do movement, plants should be adapted for harvesting dilute nutrients in environment. The adaptations give rise to specialization in plants. The specializations which occur as the consequences of being autotrophic, are as follows:

a. Plant needs an organelle which can be used to convert the inorganic molecules to be organic compounds. Thus, the plant posses a chloroplast as the organelle which will process the inorganic compounds to be organic compounds.

b. To do photosynthesis, the plant requires efficient light harvesting. Thus, they have broad leaves to maximize surface area for light harvest.

c. The photosynthesis requires an apparatus for gas exchange. The plant need to exchange the photosynthetic gasses (take up carbon dioxide and get rid of oxygen) with the environment. Thus, the leaves of plants have pores in the surface (stomata) which serves to regulate the entry/exit of gasses and prevent the loss of excessive water.

d. The plants need thin leaves for light absorption and gas exchange. Within the thin leaf, most chloroplasts are found in the upper layer of cells, the palisade layer, which is the tissue layer just beneath the epidermis. This makes “sense” since these cells will be receiving the greatest amount of light of any region in the leaf. Besides that, the advantage of having large leave is that they provide lots of surface area for absorption of carbon dioxide.

e. The plant requires a water supply to do photosynthesis. Since the plant can not do locomotion as animals, they must have an organ to help fulfill their need of water. Accordingly, plant posses “roots” which serves to obtain water from soil. A specialized tissue of the root which serves to transport the water from soil is called xylem.

f. The plant requires a mechanism to transport end products of photosynthesis throughout the plant. Thus, the plant posses phloem tissue enable the transportation of carbohydrate (as the result of photosynthesis) from leaves to roots, fruits, and other tissues where required.

  1. How do plants exploit their environment? Consider dendritic form, asexual reproduction, indeterminate growth, heterophylly, foraging and architectural design in your response.

Answer:

The inability of plant to escape an unfavorable environment has resulted in the evolution of developmental strategies that allow for flexibility in responding to local environmental fluctuations. This ability is reflected from the ability of plants to exploit their environment. The way of plants to exploit their environment are as follows:

a. Plants are dendritic

Dendritic means “tree-like” or “filamentous”. The advantage of this shape is that it provides a large surface-to-volume (s/v) ratio which enables a plant to exploit a large area of the environment.

b. Plants have indeterminate growth

Indeterminate growth is the process by which a plant continous to grow and get larger throughout its life cycle. The advantage of this is that it allows the plant, especially roots, to grow into new areas.

c. Plants have an architectural design

The body of plant is constructed like a building. It is built of a limited number of units, each of which is relatively independent of the others and that are united into a single structure. The leaves, stems, and roots of plant are analogous to a room in the building. Each room is somewhat independent, yet they all function together to make an integrated whole.

Because of their indeterminate growth and architectural design, plants are not limited by size. This gives plants the ability to colonies and exploit new areas for resources.

Because of indeterminate growth, plants are not a static shape. Plants constantly change shape by adding/loosing parts. Thus, growth in plants occurs by the addition of new units”.

d. Plants have a well-developed ability to reproduced asexually

Asexual reproduction is the way of reproduction which will be done by the plant at the plant in a though condition. This can be viewed as a quick and energetically inexpensive way to expand the influence of the parent into a new location. Plants under nutrient stress should increase their rate of asexual reproduction.

e. Plants (may) exhibit heterophylly

Heterophylly refers to leaves with different shapes. Sun leaves are tend to be smaller than shade leaves. The smaller leaves functions to reduce transpiration. Meanwhile, the shade leaves which is bigger, serves to obtain more light for photosynthesis.

f. Plants can forage

The growth pattern of plants, especially vines and plants with stolons (runners), are similar to the foraging tactics of animals. As an example, rhizomes to avoid competition.

  1. Compare and contrast animals and plants in terms of body design (i.e. architectural vs. mechanical design).

Answer: Plants typically responded by various growth movement to unpredictable, usually short-term environmental fluctuation, like changes in temperature or light. Plant usually responded to predictable, often longer-term environmental changes, like seasonal changes, by growth and developmental changes because of the constraints of their architectural design,

In contrast, animals typically respond to their environment behaviorally (by movement). Since they are motile, they can “move” to a favorable position. In fact, because they are motile, they need a nervous system to respond to the environment. Plants do not need a nervous system since they are constrained to respond to the environment by growth/developmental changes. Hence, they (plants) never had pressure to evolve a nervous system.

  1. Discuss some of the mechanisms by which plants sense changes in the environment. Why are these important?

Answer:

Plants respond to the changes in their environment in variety of ways. Those are important to be done by plants, in order that they can survive. Various response of plants to changes in environment are as follows:

a. Plants typically respond by various growth movement to unpredictable short-term environmental fluctuations, like changes in temperature or light. For example:

- some flowers like crocus are temperature sensitive and open when it is warm and close when it is cooler. The flowers of an alpine species (Gentiana algida) close up before a thunderstorm. The flowers actually respond to the decreased temperature associated with the storm front and close to avoid pollen being washed out of the flower by the rain.

- Light is one of the most important environmental cues for plant development. This phenomenon is called photomorphogenesis. The example is etiolation. Etiolation is the response of plants to growth in the dark or with reduce light. Etiolated plants are typically yellow, have elongated internodes (stems) with unfolded leaves and the stems are thinner. These features can be considered ways of conserving energy.

b. Plants usually respond to predictable, often longer-term environmental changes, like seasonal changes, by growth and developmental changes because of the constraints of their architectural design. Since this changes take time, a plant must “know” or “predict” when the environment will change and prepare for the change. Indeterminate growth is important here since it provides plants with the ability to change developmentally through the life cycle. Some example for this phenomenon include: preparing for winter (by forming buds in summer) and photoperiodism (timing flowering so the appropriate pollinator is available and that the seeds have enough time to develop before winter), nyctinasty (sleep movements), and circadian rhythms (various types in response to day/night).

  1. Identify some of the physical and biological threats to plants. How do plants protect themselves from these dangers?

Answer:

a. Physical Danger

Wind, water (flood), drought, cold (winter), are among of the physical dangers that a plant faces. In general. Plants cope with these (at least the predictable ones like winter and drought during summer) by dormancy, senescence, and even death. The evergreen and deciduous lifestyle are in part a response to adverse conditions. Evergreens are much better able to tolerate cold, dry conditions. They also do better in poor soil because they don’t loose as many leaves. Plants also respond to environmental challenges morphologically. For instance, Arctic and montane herbs are small and hug the ground.

b. Biological Danger

Biological dangers are living-things which are able to harmful to plants. Predators (=herbivores) and competitors (=other plants) are biological danger for plants. To protect themselves, plants have evolved as follows:

- Anatomical weapons

Anatomical weapons, such as thorns, hairs, and thick cuticle. Some plants are even “smart” enough to stop producing defences when they are out of rang of a herbivore. For example, the upper parts of Acacia trees above giraffe height produce few thorns. Similarly, holly leaves have few prickles above herbivores height.

- Chemical weapons

Plants are able to produce toxic or unpalatable chemicals to protect themselves against biological dangers. These can be inducible (produce in response to attack) or constitutive (always present).

- Mimicry

Mimicry is the process of “tricking” predators. The plants will do specialization in its morphological structure to trick predators. For instance, Alseuosmia is a non-toxic New Zealand plant that looks very similar to Wintera pseudocolorata (a toxic species).

- Armed forces

Some plants, like wild tobacco, when attacked by herbivores release volatile chemicals that summon predatory insects to the damage plants. These insects in turn, kill the herbivores. Overall, volatile chemicals play a very important role in plant defense. These chemicals, released when the plant is attacked by an herbivore serve as signals that can warn other plants that danger is imminent, can tell herbivores that the chemical defense system of the plant is ready for them and that should go pick on someone else, and the volatiles themselves help to repel the attack.

  1. How do plants find a "mate" and disperse offspring?

Answer: Plants find a mate (do gamete transfer) by relying on various pollination vectors. For example: Prior to pollination, the orchid released a fragrance that was an “aphrodisiac” for the male but once the flower was pollinated it produced a fragrance to repel him.

Fruits/seed dispersal mechanism help disperse offspring. This dispersal process can be helped by certain agents. The agents can be biotic agent (birds, mammals, insect) or a-biotic agents (wind, water, gravitation). For example: when a few fruit of Hamelia patens, a neo-tropical tree, are removed. It stimulates the rest of fruit to ripen. It essentially tells them that a dispersal agent is in the area.

  1. Discuss some of the problems unique to the plant way of life. In general how have plants responded to each of these problems?

Answer:

1. Problem: Plants can not run away from both physical and biological dangers, since they can not do motility. Thus, when conditions get though, they must “fight” it out.

To solve this problem, plants have typical adaptations, as follows:

a. To defend themselves against physical danger such as winter, the plants will do dormancy. Plants also respond to physical danger morphologically, for example: xeric plants minimize their leaves to minimize water loss; Arctic or montane herbs are small and hug the ground.

b. To defend themselves against biological dangers, such as herbivores, plants have evolved anatomical weapons (thorns, hairs, thick cuticle) and also chemical weapons (produce toxic, unpalated chemical). Besides that, some plants have also evolved “Armed Forces”, like wild tobacco, when attacked by herbivores releases volatile chemicals that summon predatory insects to the damaged plants. These insects in turn, kill the herbivores. Thus, the plants can be safe.

2. Problem: As non-motile organism, plants can not seek a mate (for gamete transfer) or easily disperse offspring.

Plants solve this problem by relying on various pollination vectors. Pollination vectors are the agents which help the process of moving the pollen grain from the anther of a stamen to the stigma of a carpel. Pollination vectors are water, wind, bee, and also butterfly. Fruits/seed dispersal mechanism help disperse offspring.

3. Problem: As non-motile organism, plants are unable to move to a more favorable location to carry out its vital function. A plant is stuck once the seed germinates.

To solve this problem, there are a few “tricks” that plants use to ensure that the seed will germinate in a favorable environment. For instance: Some seeds, like certain varieties of lettuce, require LIGHT for germination. This is a mechanism to insure that they germinate on the soil surface. Besides that, plants also do specialized dispersal mechanism to insure the seed getting into the proper place.

  1. Think about the statement "Plants are smarter than you think!"

Answer: “Plants are smarter than you think.” Before giving some arguments about this statement, the first thing that should be done is to understand the definition of “smart”. We should answer the question “What is smart?”, then observe the characteristics of plants. After that, we will be able to take conclusion whether plants are smart or not.

Webster’s dictionaries define intelligence as “the ability to cope with a new situation” or “the ability to learn or to deal with new or trying situations.” (http://www.fortunecity.com/greenfield/clearstreets/84/intell.htm). If we see the characteristics of plants, of course they have the ability to cope with new situations (environmental changes). Plants are able to do adaptations in order that they can survive. Plants make their own food (by processing inorganic molecules to be organic molecules through photosynthesis), plants defend against the biological dangers (through anatomical weapons, such as thorn, hairs, and sticks), plants produce toxic or unpalatable chemical to protect themselves from biological dangers, plants are able to sense changes in environment (such us, the forming of buds in summer to prepare for winter). These several characteristics can proof that the plants are able to adaptations to give response to their environment. Thus, the plants can cope with a new situations in environment. Finally, it can be concluded that the plants are intelligent, since they have “adaptively variable behavior.”

  1. Identify the characteristics of the plant kingdom.

Answer:

a. Plants are eukaryotic. It means that the cells of plants have nuclear membrane.

b. Plants are multicellular. It means that the body of plants consist of much cells.

c. Plants are producers, since they are photosynthetic autotrophic organisms.

d. They can do sexual reproduction (pollination) and also asexual reproduction (budding).

e. Plants do not do motility.

f. The cell walls of plants are composed of cellulose.

  1. Autotrophs are typically non-motile and heterotrophs are typically motile. Why did evolution favor this situation?

Answer: One of the aims of motility is to obtain food. Heterothrops are motile because they should search out and trapping the food which are widely dispersed, since they can not manufacture their own food (organic compound as the source of energy).

Meanwhile, plants are able to manufacture their own food through photosynthesis process. In photosynthesis, the energy of light is trapped and converted into the cemical bond energy of organic compounds such as sugar. Since the nutrients which are required by plants are “omnipotent”, there was never an evolutionary pressure for “motility”. Thus, plants are adapted for harvesting dilute nutrients that occurs everywhere, and they do not need to do motility.

  1. Explain why leaves are broad and flat.

Answer: The leaves are broad and flat to allow for efficient light harvest. The leaves are broad to maximize surface area for light harvest and they are thin since light can not penetrate too deeply into the leaf (the amount of light decreases exponentially with distance).

Within the thin leaf, most chloroplasts are found in the upper layer of cells, the palisade layer, which is the tissue layer just beneath the epidermis. Since the chloroplast mostly found in palisade layer, it makes sense that the broad leaves will be able to support photosynthesis, because it is able to increase the amount of light in any are of leaf.

  1. Compare animals and plants in terms of nutrients (type, concentration, location).

Answer:

COMPARISON OF ANIMAL AND PLANT NUTRITION

NUTRIENT

PLANT

ANIMAL

Type

Inorganic (CO2, H2O, ions)

Organic (proteins, carbohydrate, fats).

Concentration

Dilute

Concentrated

Distribution (Location)

Omnipotent

Localized

One of the main reasons for motility is to obtain food. Because the animals are not able to make their own food, they are adapted for searching out and trapping widely disperse, concentrated packets of food.

Meanwhile, plants are able to make their own food by processing inorganic material to be organic materials. Since the nutrients required by plants are “omnipotent”, there was never an evolutionary pressure for “motility” in plants. Accordingly, plants must be adapted for harvesting dilute nutrients that occur everywhere in its environment.

  1. Explain why plants are not limited by size.

Answer: Plants are not limited by size because of their indeterminate growth and architectural growth. Indeterminate growth is the process by which a plant continues to grow and get larger throughout its life cycle. Thus, it allows the plant, especially root, to grow into new areas. Meanwhile, architectural design means that the plant body is constructed like a building. It is built of a limited number of units, each of which is relatively independent of the others and that are united into a single structure.

This architectural growth and indeterminate growth give the plants the ability to colonize and exploit new areas for resources.

  1. Identify the specialized structures (and their function) that plants use for autotrophism.

Answer:

1. Chloroplast.

It is used by plant as the organelle in which the photosynthesis occurs. Within the chloroplast, the specialization was also required. There are three major area in the chloroplast, those are the stroma, inner membrane, and inter-membrane space. Each of these three regions is important for the functioning of photosynthesis. Electron transfer reactions occurs in the inner membrane, the calvin cycle occurs in the stroma, and the inter-membrane space is needed to generate the pH gradient across the membrane that is important for photophosphorilation.

2. Broad and flat leaves.

Leaves are the common place for photosynthesis. They are broad and flat to allow for efficient light harvest.

3. Cuticle

A waxy coating (cuticle)over the outer cell layers (epidermis), which acts to limit the amount of water loss from the leaf, as well as limiting the entry of disease organism into the leaf.

4. Stomata

Small openings in the surface of the leaf, known as stomata, whose size is regulated by specialized pairs of guard cells. These small opening allow the entry of carbon dioxide into the inner leaf structure and the release of oxygen and water vapor from the leaf to its environment.

5. Palisade tissue

It is a layer of cells that contains large concentrations of chloroplasts. This layer lies just underneath the upper epidermis and is the principal tissue involved in the photosynthetic process.

6. Spongy tissue

A loosely packed layer of cells (spongy layer) that allows free movement of gases to the photosynthetic cells of the leaf.

7. Xylem and phloem

The evolution of vascular tissue, specifically phloem, permitted movement of the result of photosynthesis from leaves to roots, fruits, and other tissues where required. Meanwhile, the xylem permitted movement of

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