Английский язык

Variant 2

I. Read the text and answer the questions in written form.

Cells: the smallest units of life differences in plants.

1. There are some structures in plant cells that are not found in animal cells. The easiest to see is the cell wall made of cellulose, which is deposited in layers around the outside of the outer cell membrane. The layer between two neighbouring cell walls is called the middle lamella and is made of calcium pectate. Cellulose is a tough but flexible material made up of long, cross-linked chains of glucose molecules.
2. Some plant cell walls are further strengthened by another material called lignin which is laid on the top of the cellulose cell wall. Water-conducting cells (Xylem) are strengthened like this and form the wood that makes up the main part of a tree trunk. Most of the woody cells are dead and hollow and consist only of the wall.
3. Much of a plant cell consists of a fluid-filled space, the vacuole, one of whose functions is to keep the cell “inflated”. The vacuole contains a solution called cell sap. In some plants this may be colored, such as the red sap in beetroots. The colors in some flowers, especially red and blue ones, are due to colored cell sap in the cells of the petals.
4. Many plant cells also contain chloroplasts. These are oval structures that contain chlorophyll, the green pigment which gives plants their color and is essential for photosynthesis. Chloroplasts can be seen clearly with the ordinary light microscope.
5. Plant cells have different shapes according to the jobs they do. Xylem and phloem are long because they form systems of tubes that transport substances through the plant. Some cells are specialized as fibres, which strengthen the plant. Root cells have thread-like outgrowths called root hairs, which absorb water and mineral salts.

Questions:

1. What structures are not found in animal cells?
2. What is cellulose?
3. How are water-conducting cells (Xylem) strengthened?
4....