Despite not havingsense organs plants can also sense things and respond to them. Plants respond to things like light, gravity, touch, water etc. These are environmental stimuli for a plant. Plants coordinate their behaviour by using their hormones and respond to the environmental changes. This they do by affecting the growth of a plant.
Therefore, pants use only hormones to coordinate their behaviour. They respond to the stimuli very slowly because they have no nervous system. Plant hormones are called phytohormones.
Dormancy: Theinactive condition of a part of a plant in which metabolism almost stops is called dormancy. For example, seed, bud etc.
The control and coordination system in plants is done by plant hormones. They affect the growth of a plant in one or the other aspect. The growth of a plant is divided in three stages:
i) Cell division
ii) Cell enlargement
iii) Cell differentiation
So, a plant hormone not only controls these stages of plant growth but also promotion of breaking of dormancy, falling of leaves, fruit growth, ripening of fruits, ageing of plants etc.
The four types of plant hormones responsible for control and coordination in plants are:
4) Abscisic acid (ABA)
While auxins, gibberellins and cytokinins promote the growth of a plant, abscisic acid prevents or hampers the growth of a plant.
Auxins hormone controls a plant response to light and gravity. It is made by the cells present at the tip of a stem and roots. This hormone moves the plant away from light and towards gravity. It speeds up the growth of stem and slows down the growth of roots.
This diagram explains the bending of a plant stem or shoot towards light by the action of ‘auxin hormone’.
Auxins promote cell enlargement, cell differentiation and fruit growth.
Gibberellins hormone works in the presence of auxin hormone and promotes cell enlargement and cell differentiation. It also promotes fruit growth, elongation of shoots and in breaking the dormancy in seeds and buds.
This hormone promotes cells division in plants and breaks dormancy in seeds and buds. They also delay ageing in leaves and promotes the opening of stomata.
This hormone inhibits the growth of a plant. Therefore abscisic acid promotes dormancy in seeds and buds. It promotes closing of stomata, wilting and falling of leave and detachment of fruit and flower from the plant.
Plants are fixed at one place and cannot physically move from one place to another. But plants still show movement by using hormones under the influence of stimuli. This movement is noticed in the unequal growth of the two regions of a plant.
For example, auxin hormone speeds up the growth of a stem. So if one side of a stem has more auxin hormone than the other, then the side of stem which has more hormones will bend. This shows movement of a plant.
Plant movement due to external stimuli are of two types: tropism and nasties.
When the direction of external stimulus decides the direction of response in the form of growth it is called tropism. Thus, tropism is the directional growth movement of a plant part. It can be in the direction of the stimulus or away from the stimulus. Therefore,
- If the growth of a plant is in the direction of stimulus, it is called positive tropism.
- If the growth of a plant is in the opposite direction or away from that of a stimulus, it is called negative stimulus.
Types of tropism
There are five stimuli in the environment. They are light, gravity, chemical, water and touch. These stimuli give five types of tropism. They are phototropism, geotropism, chemotropism, hydrotropism and thigmotropism.
When a plant part moves in response to light, it is called phototropism. If the stem of a growing plant moves or bends towards light, it is positive phototropism and if the root of a plant moves away from light, this means the roots of a plant shows negative phototropism.
When a plant part moves in response to gravity, it is called geotropism. For example, roots of a plant moves in a downward direction, so they show positive geotropism and stem moves in the upward direction, so it shows negative geotropism.
When a plant part moves in response to chemical stimulus, it is called chemotropism. Here the stimulus is chemical. For example, the growth of pollen tube towards the ovule during fertilisation in a flower is called positive chemotropism.
When a plant part moves in response to water, it is called hydrotropism. Here the stimulus is water. Roots of a plant moves towards water, so they show positive hydrotropism.
When a plant part shows directional movement in response to the touch of an object, it is called thigmotropism. For example, tendrils of a plant climb towards any support which they touch.
Response of plants to light: Phototropism
The stem and leaves of a plant moves in the direction of sunlight. So, when a plant is grown in an open ground where sunlight is coming from above then the stem of a plant grows straight in an upward direction. If, however, a plant is kept at a place where sunlight is coming from only one direction then the stem of a plant bends in that direction only. On the other hand roots of a plant bend away from the direction of sunlight.
We will perform an experiment to show this. A potted plant is kept in the open ground where sunlight is coming from above. So the stem of a plant grows straight up and roots also grow straight but in downward direction. Now, we keep this pot having straight stem and roots is kept in a dark room near a window with sunlight coming from only one side (right). After a few days we observe that stem of a plant responds to light and move towards right side and roots of the plant move towards left side that is away from sunlight.
To show the response of a plant to light (Phototropism)
This happens because of the action of auxin hormone.
- When the sunlight is coming from top, then the auxin hormone present at the tip of the stem spreads uniformly down the stem making it grow straight up.
- When the sunlight falls only on right side then the auxin hormone prefers to stay in shade and collects on left side.
- Since there is more auxin hormone on the left side of the stem, it makes left side grow faster than the right side. Thus, the stem bends towards right.
- Auxin hormone has opposite effect on the roots of a plant. That is why when sunlight falls on the right side of the roots, auxin hormone collects on the left side and hampers their growth from that side. That is why, roots bend towards left.
Response of plants to gravity: Geotropism
Roots of the plant grow towards the earth which shows positive geotropism and stem grows upward away from the pull of gravity which shows negative geotropism. This can be shown through an experiment.
- Keep a potted plant in a normal position. We see that the roots are growing downwards and stem is growing upwards.
- Now tilt the potted plant and keep it horizontally on the surface.
- After a few days we notice that roots of the potted plant grow toward the earth and stem of the plant bends upwards away from the pull of gravity.
This diagram shows the response of a plant to gravity or geotropism.
Response of plants to chemicals: Chemotropism
Sugary substance acts as a stimulus for the growth of pollen tube towards the ovule. This happens because ripe stigma in the carpel of a flower secrets a chemical substance into the style towards the ovary. This sugary substance acts as a stimulus for the pollen grain which responds by growing a pollen tube in the downward direction into the style of a carpel and reaches the ovule of the flower for fertilisation.
This diagram shows the response of a plant part ‘pollen’to chemical secreted by stigma or chemotropism.
Response of plants to water: Hydrotropism
Roots always grow in the direction of water, even if they have to grow against the pull of gravity or sideways. This can be shown through an experiment.
Let’s take two glass troughs and fill two-third of them with soil. In both the troughs we plant a tiny seedling. In the second trough we place a small clay pot inside the soil. Let’s water the soil in the first trough daily and put water in the clay pot placed inside the soil in second trough.
An experiment to show the response of a plant to water or hydrotropism.
After a few days, dig up the seedling from both troughs. We will notice that roots of the seedling of first trough are straight and that of the second trough in which clay pot filled with water was placed have bent towards the side at which clay pot was placed.
This shows that roots of a plant grow towards water.
Directional response of a plant to the touch of an object: Thigmotropism
There are some plants which cannot stand upright on their own and need support. These plants are called climbing plants and have organs called tendrils. Tendrils are the thin thread-like growth on the stems and leaves of the climbing plants. Tendrils are sensitive to the touch of other object. When tendrils come in contact with other object, it bends towards the object by growing towards it, wind around the object and cling to it. This winding movement of a climbing plant is called thigmotropism.
This diagram shows the response of a plant part ‘tendril’to the touch of an object here a bamboo stick.
For example, bitter gourd, bottle gourd, grape vine etc., have stem tendrils and peas, glory lily etc., have leaf tendrils.
The Usefulness of Tropic Movements
Tropic movements help the plant to survive. For example, roots of the plant are positively geotropic and that is the reason that they will always downward into the earth even if they are planted upside down. Also the root will grow towards water as it is positively hydrotropic. Also the shoot will grow upward as it is negatively geotropic.
Nasties or Nastic Movements
When the direction of response in a plant is not determined by the direction of stimulus, it is called nastic movement. Nastic movement is not the directional movement of the plant part.
In nastic movement, whatever be the direction of stimulus, all the parts of the plant equally move in the same direction. This type of movement is generally seen in leaves, flower petals etc.
This diagram shows the nastic movements in the leaves of sensitive plant (Mimosa pudica) caused by ‘touch’.
Following are the examples of nastic movement:
- When we touch the leaves of a sensitive plant like mimosa pudica, they fold.
- It is due to the stimulus of light that the petals of dandelion flower open in the morning and close in the evening.
- It is due to the stimulus of light that the petals of moonflower close in the morning and open in dark at night.
Nastic movement may or may not be a growth movement.
The movement of a plant part in response to the touch of an object is called thigmonasty. In this case the movement of a plant part is non-directional. The stimulus for thigmonasty is touch.
The sensitive plant mimosa pudica which is also known as touch-me-not is an example of thigmonasty. If we touch the leaves of this plant they fold up immediately and droop.
The sensitive plant has pulvini at the base of each leaf. This pulvini contains a lot of water in their cells and due to internal pressure of water they are firm and keep the leaf upright. So, as soon as we touch the leaves there is sudden loss of water from pad-like swellings (pulvini). This is why pulvini lose its firmness and leaves droop.
When we touch the sensitive place electric impulses travel through the cells of the plant and act on plant hormone. The plant hormone migrate water from the cells of the pulvinus to the intercellular spaces of the other half of pulvinus. This loss of water makes pulvini lose firmness and thus its leaves droop.
After 15 to 30 minutes water comes back to the cells and leaf gets back to its original shape.
The leaves of sensitive plant fold due to the loss of water from pulvinus at their base.
The movement of a plant part, usually flower petals, in response to light is called photonasty. The movement is non-directional. The stimulus in photonasty is light. Dandelion and moonflower are examples of photonasty.
The opening and closing of flower petals in response to light are growth movements. This is because petals open when their outer surface grows and petals close when their outer surface grows.
Function of Plant Hormones
- Germination of seeds
- Growth of roots, stem and leaves
- Movement of stomata
- Flowering of plants
- Ripening of fruits
- Tropism and nastic movements
Image courtesy: www.photos.metrojacksonville.com
- Identify coordination and subordination in writing.
- Combine sentences and ideas using coordination.
- Combine sentences and ideas using subordination.
In the previous section, we learned how to use different patterns to create sentence variety and to add emphasis to important points in our writing. Next, we will examine two ways in which we can join sentences with related ideas:
Connecting sentences with coordinate or subordinate clauses creates more coherent paragraphs, and in turn, produces more effective writing. In this section, you will read excerpts from Naomi’s classmate named Joshua, who drafted an essay about wine production. Read this excerpt from Joshua’s essay.
This section examines several ways to combine sentences with coordination and subordination, using Joshua’s essay as an example.
Coordination joins two independent clauses that contain related ideas of equal importance.
Original sentences: I spent my entire paycheck last week. I am staying home this weekend.
In their current form, these sentences contain two separate ideas that may or may not be related. Am I staying home this week because I spent my paycheck, or is there another reason for my lack of enthusiasm to leave the house? To indicate a relationship between the two ideas, we can use the coordinating conjunction so:
Revised sentence: I spent my entire paycheck last week, so I am staying home this weekend.
The revised sentence illustrates that the two ideas are connected. Notice that the sentence retains two independent clauses (I spent my entire paycheck; I am staying home this weekend) because each can stand alone as a complete idea.
A coordinating conjunction is a word that joins two independent clauses. The most common coordinating conjunctions are for, and, nor, but, or, yet, and so. Note that a comma precedes the coordinating conjunction when joining two clauses.
|Independent Clause||Coordinating Conjunction||Independent Clause||Revised Sentence|
|I will not be attending the dance.||for (indicates a reason or cause)||I have no one to go with.||I will not be attending the dance, for I have no one to go with.|
|I plan to stay home.||and (joins two ideas)||I will complete an essay for class.||I plan to stay home, and I will complete an essay for class.|
|Jessie isn’t going to be at the dance.||nor (indicates a negative)||Tom won’t be there either.||Jessie isn’t going to be at the dance, nor will Tom be there.|
|The fundraisers are hoping for a record-breaking attendance.||but (indicates a contrast)||I don’t think many people are going.||The fundraisers are hoping for a record-breaking attendance, but I don’t think many people are going.|
|I might go to the next fundraising event.||or (offers an alternative)||I might donate some money to the cause.||I might go to the next fundraising event, or I might donate some money to the cause.|
|My parents are worried that I am antisocial.||yet (indicates a reason)||I have many friends at school.||My parents are worried that I am antisocial, yet I have many friends at school.|
|Buying a new dress is expensive.||so (indicates a result)||By staying home I will save money.||Buying a new dress is expensive, so by staying home I will save money.|
To help you remember the seven coordinating conjunctions, think of the acronym FANBOYS: for, and, nor, but, or, yet, so. Remember that when you use a coordinating conjunction in a sentence, a comma should precede it.
Another method of joining two independent clauses with related and equal ideas is to use a conjunctive adverb and a semicolon (see Chapter 2 “Writing Basics: What Makes a Good Sentence?” for information on semicolon usage). A conjunctive adverb is a linking word that demonstrates a relationship between two clauses. Read the following sentences:
Original sentences: Bridget wants to take part in the next Olympics. She trains every day.
Since these sentences contain two equal and related ideas, they may be joined using a conjunctive adverb. Now, read the revised sentence:
Revised sentence: Bridget wants to take part in the next Olympics; therefore, she trains every day.
The revised sentence explains the relationship between Bridget’s desire to take part in the next Olympics and her daily training. Notice that the conjunctive adverb comes after a semicolon that separates the two clauses and is followed by a comma.
Review the following chart of some common conjunctive adverbs with examples of how they are used:
|Addition||also, furthermore, moreover, besides||Alicia was late for class and stuck in traffic; furthermore, her shoe heel had broken and she had forgotten her lunch.|
|Comparison||similarly, likewise||Recycling aluminum cans is beneficial to the environment; similarly, reusing plastic bags and switching off lights reduces waste.|
|Contrast||instead, however, conversely||Most people do not walk to work; instead, they drive or take the train.|
|Emphasis||namely, certainly, indeed||The Siberian tiger is a rare creature; indeed, there are fewer than five hundred left in the wild.|
|Cause and Effect||accordingly, consequently, hence, thus||I missed my train this morning; consequently, I was late for my meeting.|
|Time||finally, next, subsequently, then||Tim crossed the barrier, jumped over the wall, and pushed through the hole in the fence; finally, he made it to the station.|
Take a look at Joshua’s essay on wine production and identify some areas in which he might use coordination.
Now look at Joshua’s revised essay. Did you coordinate the same sentences? You may find that your answers are different because there are usually several ways to join two independent clauses.
Combine each sentence pair into a single sentence using either a coordinating conjunction or a conjunctive adverb. Then copy the combined sentence onto your own sheet of paper.
- Pets are not allowed in Mr. Taylor’s building. He owns several cats and a parrot.
- New legislation prevents drivers from sending or reading text messages while driving. Many people continue to use their phones illegally.
- The coroner concluded that the young man had taken a lethal concoction of drugs. By the time his relatives found him, nothing could be done.
- Amphibians are vertebrates that live on land and in the water. Flatworms are invertebrates that live only in water.
- Ashley carefully fed and watered her tomato plants all summer. The tomatoes grew juicy and ripe.
- When he lost his car key, Simon attempted to open the door with a wire hanger, a credit card, and a paper clip. He called the manufacturer for advice.
Please share with a classmate and compare your answers.
Writing at Work
When writing an essay or a report, it is important that you do not use excessive coordination. Workplace documents should be clear and concise, so only join two clauses that are logically connected and can work together to make one main point. If you repeat the same coordinating conjunction several times in a sentence, you are probably including more than one idea. This may make it difficult for readers to pick out the most important information in each sentence.
Subordination joins two sentences with related ideas by merging them into a main clause (a complete sentence) and a dependent clause (a construction that relies on the main clause to complete its meaning). Coordination allows a writer to give equal weight to the two ideas that are being combined, and subordination enables a writer to emphasize one idea over the other. Take a look at the following sentences:
Original sentences: Tracy stopped to help the injured man. She would be late for work.
To illustrate that these two ideas are related, we can rewrite them as a single sentence using the subordinating conjunction even though.
Revised sentence: Even though Tracy would be late for work, she stopped to help the injured man.
In the revised version, we now have an independent clause (she stopped to help the injured man) that stands as a complete sentence and a dependent clause (even though Tracy would be late for work) that is subordinate to the main clause. Notice that the revised sentence emphasizes the fact that Tracy stopped to help the injured man, rather than the fact she would be late for work. We could also write the sentence this way:
Revised sentence: Tracy stopped to help the injured man even though she would be late for work.
The meaning remains the same in both sentences, with the subordinating conjunction even though introducing the dependent clause.
To punctuate sentences correctly, look at the position of the main clause and the subordinate clause. If a subordinate clause precedes the main clause, use a comma. If the subordinate clause follows the main cause, no punctuation is required.
A subordinating conjunction is a word that joins a subordinate (dependent) clause to a main (independent) clause. Review the following chart of some common subordinating conjunctions and examples of how they are used:
|Concession||although, while, though, whereas, even though||Sarah completed her report even though she had to stay late to get it done.|
|Condition||if, unless, until||Until we know what is causing the problem, we will not be able to fix it.|
|Manner||as if, as, though||Everyone in the conference room stopped talking at once, as though they had been stunned into silence.|
|Place||where, wherever||Rita is in San Jose where she has several important client meetings.|
|Reason||because, since, so that, in order that||Because the air conditioning was turned up so high, everyone in the office wore sweaters.|
|Time||after, before, while, once, when||After the meeting had finished, we all went to lunch.|
Take a look at the excerpt from Joshua’s essay and identify some areas in which he might use subordination.
Now look at Joshua’s revised essay and compare your answers. You will probably notice that there are many different ways to subordinate sentences.
Combine each sentence pair into a single sentence using a subordinating conjunction and then copy the combined sentence onto your own sheet of paper.
- Jake is going to Mexico. There are beautiful beaches in Mexico.
- A snowstorm disrupted traffic all over the east coast. There will be long delivery delays this week.
- My neighbor had his television volume turned up too high. I banged on his door and asked him to keep the noise down.
- Jessica prepared the potato salad and the sautéed vegetables. Ashley marinated the chicken.
- Romeo poisons himself. Juliet awakes to find Romeo dead and stabs herself with a dagger.
Copy the paragraph from Joshua’s essay onto your own sheet of paper. Then edit using the techniques you have learned in this section. Join the underlined sentences using coordination or subordination. Check your revised sentences for punctuation.
- Coordination and subordination join two sentences with related ideas.
- Coordination joins sentences with related and equal ideas, whereas subordination joins sentences with related but unequal ideas.
- Sentences can be coordinated using either a coordinating conjunction and a comma or a conjunctive adverb and a semicolon.
- Subordinate sentences are characterized by the use of a subordinate conjunction.
- In a subordinate sentence, a comma is used to separate the main clause from the dependent clause if the dependent clause is placed at the beginning of the sentence.
This is a derivative of Writing for Success by a publisher who has requested that they and the original author not receive attribution, originally released and is used under CC BY-NC-SA. This work, unless otherwise expressly stated, is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.