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Introduction. All organisms are composed by cells and this is why it is so important to know what cells are and how they work. In fact, still, it is not entirely known how they work and how they control of themselves when they get to do one thing and when they have to stop. The cells, they do it, and this is sufficient, but when they stop, degenerative diseases start, such as cancer, in which cells never stop dividing which cause the death of the organism. The world of cells is an exciting world, full of mysteries in which, practically every year great discoveries are made. This topic explains all of it.
Activities to do. Read the explanations on the cell and tissue and perform the Multiple Choice Test 10.1. Then read the text on three vital functions and perform Multiple Choice Test 10.2, Crossword 10 and Complete Sentences 10.
1 . The cell. It is the simplest known living creature, meaning that it is able to perform the three vital functions, which are nourish, interaction and reproduction. It consists of two parts that are the plasma membrane and the cytoplasm.
- Plasma membrane. It is the layer that defines the cell. It regulates entries and exits of substances.
- Cytoplasm. It is the content of the cell. In it can be differentiate fluid called plasma or cytosol and a series of structures called cellular organelles. The main ones are the ribosomes, vacuoles, mitochondria, endoplasmic reticulum, the Golgi apparatus and only in cell that make photosynthesis - chloroplasts.
Inside the cell there is one or more molecules of a substance called DNA. Those are very extended molecules, so long that they look like a sewing thread, containing genetic information, which is the information of what it is and how it works. A copy of these molecules is passed to each of the daughter cells, so that they may exist. According to the DNA molecules are dispersed in the cytosol or surrounded by a special membrane forming a structure called the core, there are two types of cells, prokaryotes and eukaryotes.
Prokaryotic cells. Are the cells that have no core, which means that are those with more or less condensed DNA, inside the region of cytoplasm but without being surrounded by a membrane. The most important example of prokaryotes is bacteria cells. They are very simple cells, their organelles are practically only ribosomes, mesosomes (organelles unique to those cells) and some also have a very simple flagella.
Eukaryotic cells. These are the cells that have a core, is to say, are those with their DNA surrounded by a membrane. Animals, plants, algae, fungi and protozoa have a eukaryotic structure.
2 . The eukaryotic cell. It can be defined as a biological structure constituted by three parts called plasma membrane, cytoplasm and core, and which is capable of performing the three vital functions. The eukaryotic cell is the structural and functional unit of all multicellular organisms. It presents very different shapes and sizes. They generally have a measure of about 0,020mm, but some eukaryotic cells, such as yolk of the chicken egg have more than one centimeter of diameter.
3
. Types of the eukaryotic cells. There are two main types,
which are the ones that constitute the animals and plants.
• Animal cells. Are characterized by not having secretion or membrane, but if presented - never in cellulose, for having very small vacuoles, for the lack of chloroplasts and for the presence of centrosome, an organelle related to the presence of cilia and flagella.
• Plant cells.
Are characterized
by presenting a thick wall of cellulose on the outside (on the plasma
membrane), by
large vacuoles and
chloroplasts (they are the green organelles, because they contend chlorophyll,
which is the substance through which photosynthesize is performed) and
they have no cilia nor flagella.
4. Tissues.
It is a set of specialized cells performing a certain activity.
For example coating surfaces as epithelial tissue does or shrink how muscle
tissue does.
Connect
drawings with names. (Spanish
activity. Activity in English is under construction)
5. The role of nutrition. It is the function of matter and
energy capture.
• Autotrophic
nutrition. It is nutrition which is incorporated in the inorganic
matter. If it is done with the light energy, is called photosynthesis,
if with energy released in chemical reactions - chemosynthesis. Photosynthetic
organisms are algae, plants and certain bacteria. Chemosynthetic
organisms are few types of bacteria. In photosynthesis done by algae
and plants, oxygen is released. The chemical reaction of photosynthesis
is:
Inorganic
matter
(carbon
dioxide
+ water)
Organic
matter
oxygen
• Heterotrophic nutrition. It is a nutrition in which organic matter is captured. In nature, this matter is only produced by living organisms, therefore feeding on organic matter mean feeding on other organisms, dead or alive. In a first phase occurs digestion of food until reaching small molecules (nutrients) being able to enter the cell. Inside them, in organelles called mitochondria, they react with oxygen (known as cellular respiration) and release the energy to be alive. The rest of molecules of nutrients are used to create energy reserves or to generate structures and by that, to grow. The chemical reaction of cellular respiration is:
(carbon dioxide + water)
6 . The function of relationship. It is a capture of stimulations and emission of answers.
• The stimulants may be chemical, tactile, luminous or acoustic.
• The responses may be movements, secretions or simply directional growth, as with plant roots, due to the water (chemicotropism) or with branches due to light (fototropism).
7 . The function of reproduction. It is the generation of new individuals. There are two types of reproduction: asexual and sexual reproduction.
8. Asexual reproduction. Is the one in which the descendants are genetically identical to the parent, is to say they have the same information in their DNA. An example of asexual reproduction is that branch of geranium breaks and plant in the ground. After a time the branch generates roots and forms a new geranium. In asexual reproduction there is only one progenitor and cell multiplication process in which the daughter cells are identical to the parent cell. This type of cell division is called mitosis.
• Type of asexual reproduction in unicellular organisms. Depending on how the cell it is divided, there is bipartition, gemmation and sporulation.
Bipartition
Gemmation
Sporulation
• Type of asexual reproduction in multicellular organisms. It basically consists of a fragment of the parent who grows and gives rise to a new individual. There are reproductions by cuttings as with geranium, tubers as with potato, bulbs as with onion and gemation as with polyps.
9. Sexual reproduction. It is the one in which the descants are genetically different from their parent and also different between siblings. Is performed by special cells called sex cells that have only half of genetic information which is different in each of them. Sex cells originate by a special cell division called meiosis. There are two types of sex cells: gametes and sexual spores.
•Sexual reproduction by gametes. It is done by union (fertilization) of a male gamete with a female gamete. This gives rise to a cell (zygote) that already has the complete genetic information. The zygote, by multiplication, gives rise to an embryo and afterwards and entire new individual. The animal male gametes are called spermatozoa and plants - antherozoid. The animal female gametes are called ova, and plants - oosphere. Fertilization can be external or internal, depending on the copulatory organs. In animals the embryonic development may occur within an egg (oviparous) or within the maternal body (viviparous).
• Reproduction through sexual spores. In it, a single spore
generates a whole new individual. It occurs in fungi and plants. In plants
the sexual reproduction by gametes is alternate by spores.
• Alternate reproduction. It occurs, for example, in some species of jellyfish. It alternates sexual reproduction by gametes with asexual reproduction through fragmentation.
Biology
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