- Xylem contains tracheids, vessels, xylem parenchyma and xylem fibre.
- Tracheids: They are elongated, tubular dead cells with tapering end walls.
- Vessels: These are also known as trachea. They are elongated, tubular dead cells. They are joined to each other by end to end forming a continuous pipe. The cells are thick and lignified.
- Xylem parenchyma: They are also called wood parenchyma. This is the only living tissue of xylem.
- Xylem fibre: They are dead cells with thick walled fibre.
- Phloem consists of sieve tubes, companion cells, phloem parenchyma and phloem fibres.
- Sieve tubes: These are elongated, tubular living cells arranged in a row, with their perforated end walls forming a sieve. They are non-nucleated. Their protoplasm are inter-connected through sieve plates. They possess vacuoles.
- Companion cell: They are elongated, lens-shaped cells containing dense cytoplasm and prominent nuclei. These cells maintain connection with sieve cells through pits.
- Phloem parenchyma: They are living thin walled parenchyma cells.
- Phloem fibre: They are also known as bast fibre. They are elongated fibre like sclerenchymatous dead cells with thick walls containing pits and interlocked ends. Phloem fibre are the only dead cells in phloem.
Hope you could get an idea from here.
Doubt clarification - use comment section.
Answer:
The correct answer would be - "bacterial populations evolve in response to the selection pressure imposed by antibiotics".
Explanation:
The given information provided in the question about the bacterial infection supports the hypothesis that the bacterial population shows the evolution in response to the selection pressure caused by the antibiotics due to the fact that bacteria increased resistance gradually with time. This resistance towards antibiotics increased the percentage of bacterially infected children in the late 1980s and early 1990s.
In this case, the population of bacteria having resistance genes is selected to evolved selected to increase their offsprings.
The right answer for the question that is being asked and shown above is that: "(4) the introduction of a species that has increased the long-term biodiversity of an ecosystem." This plant ruins fishing areas and interferes with boating and other water sports. This is an example of the introduction of a species that has increased the long-term biodiversity of an <span>ecosystem</span>