Stems are the structural axes found in plants. Here are the three functions of stems:
1. They serve as the plant’s support by holding up the leaves to the sun.
2. They are the plant’s transport system that delivers the water and nutrients into the different parts of the plant.
3. They form the branches, the leaves, and the flowers.

B. stem

Choices B, C, and D are incorrect. The encircled areas in the diagram show the areas of active plant growth. The growth is produced by the meristem tissues.

A. meristem tissue

Choices A, B, and D are incorrect. In the xylem tissue of plants, the specialized cells found are the tracheids and the vessel elements. The tracheids are the elongated cells found in the xylem tissue, while the vessel elements are the shorter and wider cells in the xylem tissue. The roots, stems, and leaves of a plant have these cells form interconnected channels in order for the water to reach all the parts of the plants. Both tracheids and vessel elements are involved in the movement of water throughout the plant.

C. xylem

Choices A, B, and D are incorrect. Phloem tissues carry the nutrients and the products of photosynthesis throughout the plant. It has sieve tube elements which are the specialized cells involved in transferring the molecules to the other parts of the plant. The activity of the sieve tube elements is regulated by companion cells.

C. transport of products of photosynthesis

Mature xylem is made up mostly of dead cells. They are involved in the movement of water and ions throughout the plant.

On the other hand, the phloem cells are alive at maturity. They carry the nutrients and the products of photosynthesis throughout the plant.

The three main functions of the leaves of a plant are the following:
1. For absorbing light and carrying out photosynthesis
2. For conducting transpiration
2. For maintaining homeostasis and facilitating in gas exchange

In order for a plant to grow, it needs energy. The movement of the sugars in the phloem ensures that the sugars are transported into the sink cell or areas where the energy is needed, particularly in a region where there is a new tissue growth.

In a monocot stem, the vascular bundles are scattered at irregular intervals throughout the tissues. On the other hand, the vascular bundles in a dicot stem resemble a ring or a doughnut pattern.

Choices B, C, and D are incorrect. Hormones are substances that serve as chemical signals that influence the activities of cells and tissues, such as growth and development.

A. hormones

Choices A, B, and D are incorrect. Cytokinins trigger cell division, growth of lateral buds, and germination of dormant seeds.

C. cytokinins

Choices A, C, and D are incorrect. Photoperiod is the term that describes the day length or the period of time each day.

B. day length

Auxins trigger vertical growth, wherein the cell elongates in response to the direction of light and gravity. On the other hand, cytokinins cause lateral growth, wherein the diameter size of a cell increases.

The term tropism is described as the movement of a living organism in response to a particular stimulus. The three types of plant tropisms include gravitropism (response to gravity), phototropism (response to light), and thigmotropism (response to touch).

The tropism that affects the stem would include thigmotropism. An example of this tropism is when a plant curls around a trellis as it grows. On the other hand, the growth of roots are mainly affected by the downward pull of gravity; hence, it exhibits gravitropism.

Photoperiodism is the plant’s response to the seasonal changes, which affect the flowering and growth of plants. Due to a pigment called phytochrome, plants can detect the differences in day length. When trees sense that there is less sunlight, the leaves start to change their colors and they fall.

Moreover, when short-day flowering plants sense that the length of the night becomes longer, the flowers begin to bloom. On the other hand, when the long-day plants detect that the length of the nights became shorter, the flowers would start to bloom.

The winter dormancy occurs when a cold temperature signals the deciduous trees to temporarily stop photosynthesis and to seal off the leaves from the rest of the tree or the plant. Aside from leaf loss, there are also changes in the apical meristems. They produce waxy scales that serve to protect the new leaf buds. In this way, the buds can survive the harsh winter climate.

Choices A, C, and D are incorrect. The development of agriculture occurred between 10,000 to 12,000 years ago.

B. 10,000 years ago

Drug discovery happens among wild plant species. If a particular species become extinct, it would also decrease the chances of finding and developing a powerful cure for diseases.

Heirloom plants are described as the plant varieties that were cultivated in the past and in ethnic communities. However, they are no longer used in large-scale agriculture at the present. Reintroducing heirloom plants would strengthen the genetic diversity among the crops. It would also reduce the occurrence of pest devastation in farms.

Dormancy is an adaptive function that allows the seeds of lupine to hinder germination when unfavorable conditions exist. As a result, this helps the seeds to survive harsh environmental conditions and allows them to grow at a later time when the situation is more ideal; hence, their seeds are preserved and their species remain for a longer period of time.

The Casparian strips, which have a hydrophobic feature that gives a wax-like texture in the cell walls of the roots, aid in the one-way or upward movement of water molecules in the vascular cylinder. This feature is an important part in producing the pressure in the roots.

If the plant root lacks the Casparian strips, it would not be able to prevent the backflow of water inside the vascular cylinder; hence, the water would return into the cortex and diffuse through the cell walls. This event would not allow the water to go into the different parts of the plant.

The possible hypothesis for this observation is that as the plants grow upward, the roots are also expanding downward.

As the plant grows upward above the surface, the roots also grow within the soil. The growth of the roots exhibits gravitropism wherein the movement goes in the direction of the gravity. Since the roots play an important part in absorbing water and nutrients for the plants, there should be enough space for the roots to grow. If they are restricted to a certain amount of soil and water, they are not able to function properly; hence, the productivity of the plant would decrease.

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 dense foliage that looks like a miniature tree.

An example of plant thigmotropism is the way the tendrils of the sweet pea curls around a trellis. This movement happens when the side of the tendril that is in contact with the object grows slower, whereas the opposite side grows faster. The slow growth of the contact side occurs due to the compression that is responsible for the curving movement. This tropism is beneficial when it comes in directing the growth pattern of a vine or other climbing plants.

The seed that contains the endosperm is a rich source of energy and nutrients. This is the reason why most plant foods come from the seeds.

Large-scale cultivation involves the use of tons of chemicals, such as pesticides and fertilizers. Here are the benefits and dangers of using pesticides and fertilizers in growing crops:

Benefits:
Fertilizers provide additional nutrients to the plants, while pesticides reduce pest infestations and diseases on the crops. Using these two substances on large-scale cultivation would increase the crop yield and production.

Dangers:
This action causes pollution that damage the soil and water conditions. More importantly, the chemicals interfere with the nutrient cycle and kill many organisms in the ecosystem.

Most of the drug discovery happens among plant species. Plants are often considered as great sources of medicines because they contain chemical compounds or active ingredients that are used in developing a powerful cure for diseases. In addition, medicinal plants are easily available and eco-friendly.

The opposite effects of gibberellins and abscisic acid in the seeds play a key role in germination and dormancy. The presence of abscisic acid in a seed would inhibit growth and trigger dormancy, whereas gibberellins signal growth and seed germination. In other words, their relationship is like an on-and-off switch. Without the presence of the other hormone, the process of germination or dormancy would not be controlled.

For example, if the abscisic acid switches on the dormancy function, the seed would switch off the germination. In this case, if the gibberellins are not present, there would be no signal that would stop the dormancy and initiate growth.

Since sunlight is directed in the equator, this indicates that countries near the equator experience 12 hours of daytime regardless of the season. This explains why areas that lie within the tropics are not suitable for growing long-day plants because their days do not get long enough.

In this case, spinach and other long day plants would grow abundantly during the summer in the temperate regions because the day length in there lasts for 14 hours or more.

Cultivating plants on gardens and farms involves the use of chemicals, such as pesticides and fertilizers. Here are the advantages and the disadvantages of using pesticides and fertilizers in growing crops:

Advantages:
Fertilizers provide additional nutrients to the plants, while pesticides reduce pest infestations and diseases on the plants. Using these two substances would increase the plant’s productivity.

Disadvantages:
This action causes pollution that damage the soil and water conditions. The chemicals interfere with the nutrient cycle and harm many organisms in the garden or farm. If the plants are used for food consumption, the traces of the chemicals would harm or poison the humans.

The experiment showed the response of the stem according to gravity.

First setup:
The pot was in an upright position. As a result, the stem grew upward, which is in the opposite direction of the gravity. This plant exhibited negative gravitropism.

Second and third setup:
When the pot is placed sideward and downward, the stem responded negatively to the downward pull of gravity. As a result, the stems were bent upright.

This possible hypothesis in this experiment is that the stem has a negative response to gravity. This was shown when the stem grew in a direction away from the gravity (negative gravitropism).

According to the experimental setup, negative gravitropism was tested by placing the potted plant in both sideward and upside down direction. When the pot is placed on a sideward or downward direction, the stem did not grow downward. Instead, the stem bent and grew toward the direction of the light, which is opposite of the gravity.

According to the experimental setup, negative gravitropism was tested by placing the potted plant in both sideward and upside down direction. However, it showed that the plants did not just grow 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 of the auxin hormones that are present in the plant. These hormones react to both light (phototropism) and gravity (gravitropism).

The main forces that are responsible for water transport in the xylem are the cohesion, adhesion, and surface tension within the water molecules and the plant tissues. These forces act during the transpirational pull which is like a suction that causes the water from the leaves to evaporate through the stomata.

Cohesion is responsible for the attraction within the the water molecules. This action allows the water to flow as a unit or a huge single molecule. Due to the cohesive forces in the water molecules, surface tension is formed. In this process, the water resists an external force and rises against gravity. This is similar to the way when the water goes up in a straw. On the other hand, adhesion refers to the way the water adheres to the xylem tissues.

The main forces that are responsible for water transport in the xylem are the cohesion, adhesion, and surface tension within the water molecules and the plant tissues. These forces act during the transpirational pull which is like a suction that causes the water from the leaves to evaporate through the stomata.

The guard cells, which are found in the stomata, contains a turgor pressure that controls the opening and closing of the stomata to regulate the rate of transpiration in plants. This mechanism helps the plants to retain water. If a plant loses too much water, it will start to wilt.

In addition, these cells also trigger the stomata to open during the day when there is a huge amount of sunlight. During the night, the stomata have a tendency to close since there is a lack of light.

According to the graph, Florida used 38 percent out of the overall use of methyl bromide in the farms and orchards in the United States. This percentage is equivalent to 10,260 tons every year.

Choices B, C, and D are incorrect. In order to compare the use of methyl bromide between Florida and other states, scientists can determine the acres of farms in each state. In this way, they can gauge the amount of chemicals that are used or applied to the farms in all states.

A. the acres of farms and orchards in each state

1. Dermal tissue – for protection
The dermal tissues serve as the outer covering of the leaf. The cells that make up the epidermis are protected by thick cell walls that resist tearing. They also have a waxy covering that helps prevent too much water loss during evaporation.

2. Vascular tissue – for transport
The vascular tissues in a leaf are connected to the vascular system of the stem. In this case, they serve the same function, which is to transfer water and nutrients throughout the plant.

3. Ground tissue – for photosynthesis
The ground tissue of a leaf is where photosynthesis takes place. These tissues fill in the area between the leaf veins.

A tuber is a plant’s modified stem that stores food and nutrients for later use. One example of a tuber is a potato. Potatoes (Solanum tuberosum) are classified as a starchy, tuberous crop that is a staple food in many parts of the world. According to history, this plant was first cultivated in Peru. Eventually, potatoes were brought by the Spanish into Europe.

Potato plants are perennial angiosperms that undergo either self-pollination or cross-pollination with the help of insects. Varieties of this plant can either be grown using seed potatoes, which are the smaller versions of the edible potato, or vegetative propagation. They can adapt to diverse climates as long as there is sufficient water supply to nourish the starchy tubers. However, it is best to plant potato crops in the early spring, particularly when the frost is gone and before the soil is fully warm. Moreover, they do not grow abundantly to heavy clay soil. These plants prefer rich, loamy soil.

Once the seed potatoes are cut, make small hills that are 1 or 2 inches high and 10 to 12 inches apart from each other. In each hill, one seed potato must be planted. The plants must be watered every week because the moisture in the soil must be maintained. However, it is important to avoid overwatering because it can saturate the soil. After 90 to 120 days, the potatoes can finally be harvested.

The main organs of plants include the roots, stems, and leaves. These three structures are responsible for the in-and-out movement of substances and materials in the plants.

Roots are hair-like structures that are formed in vascular plants. They anchor the body of the plants to the soil and help absorb the water and nutrients.

Stems are the structural axes found in plants. They serve as the plant’s support and transport system.

Leaves are the broad and flat surfaces found in plants that are used in photosynthesis. It protects the plant from water loss by retaining the water and letting the exchange of gases take place.