What are lysosomes? What are mitochondria?
Lysosomes are membrane-bounded vesicles, containing digestive enzymes. Their normal function is digestion of complex nutrients and broken-down organelles. Mitochondria are the powerhouses of the animal cell, where the products of the metabolism of nutrients are converted into energy in the form of molecule ATP. Plants possess, in addition to mitochondria, similar organelles called chloroplasts. Each chloroplast contains chlorophyll which is used to convert light energy to the ATP. This process is called photosynthesis.
All animal and some plant cells contain a pair of centrioles. Centrioles control the arrangement of microtubes in cytoskeleton.
What is the process called meiosis?
All cells are the products of division of preexisting cells. Simple cell division, or asexual reproduction, normally results in the production of two identical daughter cells. Sexual reproduction is the mingling of the DNA of two different organisms of the same species to produce cells with a new combination of genes. In multicellular organisms sexual reproduction requires the production of male and female germ cells by a process called meiosis.
In higher plants and animals the cells are organized into tissues, or groups of cells with similar structure and functions. Combinations of tissues make up organs with more or less distinct functions. In the animal; the organs are associated in systems that are responsible for certain functions.
Read the text and fill in the gaps with the words in the box.
| Cell membrane, cells, microscope, structure, nucleus, cytoplasm. |
Cells
1. … are the building blocks of living things, as bricks are of houses. Larger organisms, such as human beings, are made of billions of cells. Each cell is a tiny living unit that is too small to be seen without a 2. …. Cells usually have three main parts. The 3. … (outer "skin") controls what goes in and out of the cell. The 4. … is the area where most of the cell's reactions take place, such as the release of energy by the mitochondria. The 5. … controls all the cell's activities. Different cells do different jobs; this affects their 6. …
Read the text, make up its plan and match English words in A with their English equivalents in B
The Cell
The living things around us – plants and animals which inhabit every part of the world – differ from non-livingthings because they take in food, they grow andreproduce their kind. Animals andplants have several other activities which distinguish them from non-living things.
If we examine a very thin piece of a plant under a microscope, we'll see that it has a honeycomb structure; it is divided into a great many compartments called cells. Animal tissue, like plant tissue, is made up of cells and in large organisms the number of cells runs into many millions. In such organisms there are many types of cells; they differ in function and also in shape and size. Each cell is surrounded by a cell wall or membrane as it is generally called.
The cell walls of plants are formed of a substance called cellulose, which gives strength to the plant. Within the cell there is a thick jelly-like substance called protoplasm.
Protoplasm is the substance of which the living contents of the cell are composed. It is far more complex in its composition than cellulose, consisting of carbon, hydrogen, oxygen and nitrogen, and some other elements of which phosphorous and sulfur are the chief. It is soft and jelly-like in structure, never truly fluid. At times it is homogeneous and transparent, more often it is granular in appearance. There is always a quantity of water present, which, especially in the older cells, collects in drops or vacuoles. The protoplasm is the living part of the cell and possesses considerable power of movement.
In most living cells there is a nucleus, a rounded or oval structure embedded in the protoplasm. It plays an extremely important part in the life of the cell.
A B
To inhabit to be all around something
To distinguish to recognize the differences between things
To examine to live in a particular place
Compartment to look at something carefully
To surround to arrange the parts of something in order to get a particular effect
To compose one of the separate parts of the container or place where things are stored
Fluid to fix something firmly
Transparent the amount of something
Quantity likely to change
To possess thin enough for you to see things through
To embed to own something