A hormone is an organic substance that is secreted by an organism that affects a part of its body, or even its function.

A. hormone

Chemists have discovered that a high concentration of auxin can be used to inhibit growth in plants. This compound is used as a herbicide to kill weeds.

A. herbicides

Since auxins inhibit lateral growth, their absence produces lateral buds which eventually form into side branches. If you cut the tip of a plant more often, auxins are lessened; therefore, a plant will grow laterally. This event is called apical dominance, which is the reason for the shape of the plant on the left.

D. apical dominance

Cytokinins trigger cell division, growth of lateral buds, and germination of dormant seeds.

C. cytokinins

Gibberellins are the substances that are responsible for the dramatic increase in the size of stems and fruits.

B. gibberellin

The three types of plant tropisms include gravitropism, which is the plant’s response to gravity; phototropism, which is the way plants respond to light; and thigmotropism, which is the plant’s response to touch. Since the question asks for the plant’s response to touch, thigmotropism is the correct answer.

D. thigmotropism

Photoperiodism refers to the way plants respond to the timing of light and darkness.

B. light and darkness

Dormancy refers to the period wherein an organism is alive but it stops growing or developing.

B. dormancy

Plants that are adapted to the aquatic environment have air-filled spaces in their tissues. This allows an aquatic plant to diffuse oxygen from the air spaces to its roots.

B. aquatic plants

Epiphytes are organisms that are anchored on the surface of other plants. However, they are not parasites since they have a way of producing their own food by gathering moisture and nutrients from the rain and the air.

A. epiphytes

Auxins trigger vertical growth, wherein the cell elongates in response to the direction of light and gravity. Usually, these hormones are produced at the roots or the apical meristem of a plant. When trees grow tall and upright, there is a presence of auxins in the apical meristem.

**Phototropism** is the response of an organism like plants to the source of light. It has two kinds: ***Positive phototropism*** in which the organism moves toward the source of light and ***negative phototropism*** which moves away from it. This response is made possible through the hormones auxins

**Auxins** is considered a growth hormone in plants where it promotes growth in the shoot and root tips through initiating cell division. Auxin plays a role in the maintenance of apical dominance since the auxin moves to the darker side of the plant which will result in the cells present there growing longer than others.

If you cut the tip of a plant that contains the apical meristem, the auxins are lessened and the plant’s growth will be distributed laterally. This event is called apical dominance, which is the reason for the shape of a bonsai tree. A bonsai tree, which is pruned regularly, develops a dense foliage that looks like a miniature tree.

Tropism is the way organisms move in response to an external stimulus. Gravitropism is responsible for the upward growth of shoots into the sunlight and the downward growth of roots into the soil. On the other hand, phototropism is how the plant reacts toward the direction of the light source or away from it. In this case, the stem may bend in response to the direction of the light.

**Photoperiodism** is a physiological reaction and response of an organism like plants to the period or length of night/darkness. It is a developmental adaptation of plants to the relative period of light and darkness. And this response can affect the blooming of plants

**Photoperiodism** is a physiological reaction and response of an organism like plants to the period or length of night/darkness. It is a developmental adaptation of plants to the relative period of light and darkness. And this response can affect the blooming of plants. There are two types of plants under this condition: short-day plants, and long-day plants.

**Short-day plants** are plants that require a long period of darkness in their life cycle. These plants only produce flowers when the length of the day is less than 12 hours. Examples of short-day plants are chrysanthemums and poinsettias.

On the other hand, **long-day plants** are plant species that require more hours of exposure to sunlight than in darkness. Plants like spinach and irises are considered long-day plants because they bloom when days are longer.

**Long-day plants** are plant species that require more hours of exposure to sunlight than in darkness. Plants like spinach and irises are considered long-day plants because they bloom when days are longer.

As per the given description, arctic plants are considered **long-day plants** because they bloom during late spring when the day is longer than night.

Long-day plants

Phytochrome is a plant pigment that is mainly responsible for the process of photoperiodism. This pigment absorbs red light and triggers the changes within a plant cell.

A cold temperature signals the deciduous tree to temporarily stop photosynthesis. Because of this, the leaves start to change its color. The tree transports the nutrients from the leaves going to the roots and stores it there until a warmer temperature comes. Since the leaves are sealed off from the tree, it begins to shed and fall to the ground.

**Adaptation** is when the organism form and develops special features that would benefit the organism for a greater chance of survival in the varying environment. Adaptation is related to evolution, as this can be inherited by the offspring from its parents. Plants learned to adapt to the various environments thus increasing their ways of survival–two examples of this are the presence of aquatic plants and desert plants.

**Desert plants** are also called *xerophytes*. These plant species can withstand extreme environmental conditions such as sandy soil, intense heat, strong winds, and lesser rainfall. These plant species have **developed extensive roots, thick stems, and lesser leaf structures for the storage of water molecules in their system**.

Flowers that bloom at the same time increases the chances of spreading the pollen grains which help in pollination and fertilization.

When a seed is planted in a wrong direction, the force of gravity impacts the way a seedling will grow. In this case, since gravitropism is responsible for the upward growth of shoots into the sunlight and the downward growth of roots into the soil, the seedling will either make a turn or bend and grow according to the direction of the force of gravity.

The experiment wanted to test the hypothesis about positive and negative gravitropism. It aims to explain how the plants grew in response to gravitropism.

According to the experimental setup, negative gravitropism was tested by placing the potted plant in both sideward and upside down direction. However, it showed how the plant grew upward in a direction that is against the force of gravity but also according to the direction of light. This means that both phototropism and gravitropism are involved in this process.

It would be better if the experimental design included phototropism as one of the factors that contributed to the upward growth of the plant. Aside from gravitropism, phototropism also acted in this process. This is because the auxin hormones present in the plant caused phototropism and gravitropism.

Plant hormones are chemical signals that affect the growth, activity, and development of cells. Plant hormones play a role in cell elongation and growth of new roots; seed dormancy; cell division; growth and ripening of fruit.
Different plant hormones include auxins, gibberellins, cytokinins, Abscisic acid, and ethylene.

The plant hormone **auxins** are responsible for the growth of new roots at the tip of the shoot. **Auxins** are considered growth hormone in plants because it promotes growth in the shoot and root tips through initiating cell division. Hence, plants continue to grow as long as they are alive because of the presence of the auxin hormone.

Since sunlight is directed at the equator, this indicates that countries near the equator experience 12 hours of daytime regardless of the season. Because of this, long-day plants are not suitable to grow in a place where the sunlight exposure only lasts for a certain time. Spinach plants usually need a minimum of 14 hours of daylight exposure.

**Adaptation** is when the organism form and develops special features that would benefit the organism for a greater chance of survival in the varying environment. Adaptation is related to evolution, as this can be inherited by the offspring from its parents. Plants learned to adapt to the various environments thus increasing their ways of survival–two examples of this are the presence of aquatic plants and desert plants.

Plants were able to adapt and formed specialized features and structures that enable them to acquire nutrients especially if they are located in an environment having scarce or very few nitrogen molecules efficiently, thus explaining the presence of carnivorous plants and parasites.

As the plant begins to develop, the embryonic roots will start emerging from the seed (and this will be termed the primary root). This will allow the seed to be anchored in the soil or ground. The orientation of the seed in the soil will not matter, as the root will orient itself towards the ground through gravitational force

Hence, whether the seed was planted upside down or the other way around, it will still have the capability to arrange itself in a way that the stem will grow upward and the roots will grow downward.

climbing plants are better able to survive in a thick canopy rain forest by positioning themselves towards sunlight. Non-climbing trees can be easily overshadowed by another tree.

see explanation for solution

Plants that are adapted to the aquatic environment have air-filled spaces in their tissues. This allows an aquatic plant to diffuse oxygen from the air spaces to its roots. They also have reproductive adaptations in the form of seeds that goes through seed dormancy and float on the water’s surface until they germinate under ideal conditions.