Question

write a summary (2 page) lab report on plant evolution, angiosperm reproduction, transport systems in plants and transpiration.

Answer 1

1.

The evolution of plants has resulted in a wide range of complexity, from the earliest algal mats, through multicellular marine and freshwater green algae, terrestrial bryophytes, lycopods, and ferns, to the complex gymnosperms and angiosperms of today. While many of the earliest groups continue to thrive, as exemplified by red and green algae in marine environments, more recently derived groups have displaced previously ecologically dominant ones, e.g. the ascendance of flowering plants over gymnosperms in terrestrial environments.[6]:498

There is evidence that cyanobacteria and multicellular photosynthetic eukaryotes lived in freshwater communities on land as early as 1 billion years ago,[7] and that communities of complex, multicellular photosynthesizing organisms existed on land in the late Precambrian, around 850 million years ago.[8]

Evidence of the emergence of embryophyte land plants first occurs in the mid-Ordovician (~470 million years ago), and by the middle of the Devonian (~390 million years ago), many of the features recognized in land plants today were present, including roots and leaves. By Late Devonian (~370 million years ago) some free-sporing plants such as Archaeopteris had secondary vascular tissue that produced wood and had formed forests of tall trees. Also by late Devonian, Elkinsia, an early seed fern, had evolved seeds.[9] Evolutionary innovation continued throughout the rest of the Phanerozoic eon and still continues today. Most plant groups were relatively unscathed by the Permo-Triassic extinction event, although the structures of communities changed. This may have set the scene for the appearance of the flowering plants in the Triassic (~200 million years ago), and their later diversification in the Cretaceous and Paleogene. The latest major group of plants to evolve was the grasses, which became important in the mid-Paleogene, from around 40 million years ago. The grasses, as well as many other groups, evolved new mechanisms of metabolism to survive the low CO
2 and warm, dry conditions of the tropics over the last 10 million years.

2. Although the angiosperms are known as flowering plants, they are difficult to distinguish from gymnosperms solely on the basis of bearing flowers, for, like the strobilus, a flower is a compressed stem, with crowded spore-bearing appendages. The occurrence of colored petals and attractive scents is not essential and is by no means characteristic of all flowers. The most important distinguishing feature separating flowering plants from gymnosperms is that the ovules of flowering plants are produced within enclosed containers called carpels.

Angiosperms are able to grow in a variety of habitats. They can grow as trees, shrubs, bushes, herbs, and small flowering plants. Some of the characteristics of angiosperms include:

• All angiosperms have flowers at some stage in their life. The flowers serve as the reproductive organs for the plant, providing them a means of exchanging genetic information.
• Angiosperms have small pollen grains that spread genetic information from flower to flower. These grains are much smaller than the gametophytes, or reproductive cells, used by non-flowering plants. This small size allows the process of fertilization to occur quicker in the flowers of angiosperms and makes them more efficient at reproducing.
• All angiosperms have stamens. Stamens are the reproductive structures found in flowers that produce the pollen grains that carry the male genetic information.
• Angiosperms have much smaller female reproductive parts than non-flowering plants, allowing them to produce seeds more quickly.
• Angiosperms have carpels that enclose developing seeds that may turn into a fruit.
• A great advantage for angiosperms is the production of the endosperm. The endosperm is a material that forms after fertilization and serves as a highly nutritional food source for the developing seed and seedling.

3. Transpiration is a process that involves loss of water vapor through the stomata of plants. Transpiration is thought to be a 'necessary cost or evil' to allow the plant to absorb water from the soil. It is an inevitable process.

Transpiration is important in plants for three major reasons:

1. Cooling of the plant: the loss of water vapor from the plant cools down the plant when the weather is very hot.
2. The transpirational pull: when the plant loses water through transpiration from the leaves, water and mineral salts from the stem and roots moves, or is `pulled', upwards into the leaves. Water and is therefore taken up from the soil by osmosis and finally exits the plants through the stomata.
3. Plant structure: young plants or plants without woody stems require water for structural support. Transpiration helps maintain the turgidity in plants.

Transpirational pull results from the evaporation of water from the surfaces of the mesophyll layer in the leaf to the atmosphere, through the stomata. Evaporation of water from the leaves surface causes a negative pressure (suction force) in the xylem that pulls water from the roots and soil. This results in water being drawn up the xylem vessel.

Transpirational pull draws water from the roots to the leaves because of the effects of capillary action. The primary forces that create capillary action are adhesion and cohesion. Adhesion is the attraction that occurs between water and the surface of the xylem, and cohesion is the attraction between water molecules.

We will revisit transpirational pull and capillarity later in the chapter when we examine how water is transported in the plant.

Plants absorb water and minerals by the roots. The roots have root hair.The root hair increase the surface area of the root for the absorption of water and mineral nutrients dissolved in water. The root hair is in contact with the water present between the soil particles.Can you guess how water moves from the root to the leaves? What kind of transport system is present in plants?Plants have pipe-like vessels to transport water and nutrients from the soil. The vessels are made of special cells, forming the vascular tissue. A tissue is a group of cells that perform specialised function in an organism. The vascular tissue for the transport of water and nutrients in the plant is called the xylem.

The xylem forms a continuous network of channels that connects roots to the leaves through the stem and branches and thus transports water to the entire plant .

You know that leaves synthesise food. The food has to be transported to all parts of the plant. This is done by the vascular tissue called the phloem. Thus, xylem and phloem transport substances in plants.

Activity

Take a large potato and peel off its outer skin. Cut one of its ends to make the base flat. Now make a deep and hollow cavity on the opposite side. Fill half of the cavity with sugar solution and mark the level by inserting a pin in the wall of the potato (Fig. 11.8). Put the potato into a dish containing a small amount of water. Make sure that the level of water is below the level of the pin. Allow the apparatus to stand for a few hours.You would find an increase in the level of sugar solution. How did water get inside the potato? For very short distances water can move from one cell to another. In the same way water reaches xylem vessels of the root from the soil.