Science [3 Mark Questions]

•Position, size and nature of image formed by a convex mirror.

Position of the object	Position of the image	Size of the image	Nature of the image
At infinity	At the focus F, behind the mirror	Highly diminished, point-sized	Virtual and erect
Between infinity and the pole P of the mirror	Between P and F, behind the mirror	Diminished	Virtual and erect

When reflecting face of a mirror is made spherical, it is called a spherical mirror.

⇒ To prepare a spherical mirror, a thin spherical shell of glass is cut, parallel to any of its diameters.Then we separate the smaller part. Now if its inner face is made reflecting then we get a concave mirror and if its outer face is made reflecting then we get a convex mirror.

In above diagrams, backsides of both the mirrors are shown shaded which are non-reflecting. For a large shining spoon, its inner face can be treated nearly like a concave mirror whereas its outer face can be treated nearly like a convex mirror.

SELF

SELF

• In an exercise of tracing the family trees of species, we need to remember following things
• There are multiple branches possible at each and every stage of this process.
• Evolution is not as if one species is eliminated to give rise to a new one.
• A new species has emerged does not mean that the old species will disappear.
• It depends on the interactions with the environment.
• It is not necessary that the newly generated species are in any way better than the older one.
• Natural selection and genetic drift have together led to formation of a population that cannot reproduce with the original one.
• This creates isolation, which further lead to speciation.

• The dead bodies of plants or animals, in presence of oxygen and moisture, undergo decomposition with the help of microorganisms.
• But sometimes in certain environmental conditions their bodies or organs do not get decomposed fully.
• The dead body may be entangled in mud and the same may be covered by dry stony covering.
• This prevents the dead body to decompose further.
• The mud settles around the dead body or organ in the shape of the later, and form stony covering.
• In this stony covering the imprint of the body or the organ is formed as a fossil.
• That is why, sometimes in the earth’s crust the imprint of the dead body or the organs are maintained.

SELF

→ Rhizopus is thread like structure that is developed on bread. It produces thin, delicate fibers which are fungal filaments. The fibers form an irregular lattice. It is called hyphae.
→ Some fibers of hyphae grow in upward direction. On tip of it a round structure is observed which is known as sporangia which contain cell or spores.
→ Spores are transported by air. During the appropriate conditions they develop into new Rhizopus individuals.

→ Importance : Many spores are produced by Sporangi so they can spread very quickly

Description : A flower is the shoot of the plant converted for the process of reproduction. It is developed from a bud. Corolla gives support to the flower and four layers are arranged on thalamus.
→ (1) Sepal Layer
(2) Petal Layer
(3) Stamen Layer
(4) Pistil Layer
(1) Sepal Layer : It is made up of sepals. They are the outermost layer. They protect the flower in budding stage but they do not participate in the process of reproduction.
(2) Petal Layer : It is the second layer. It attracts the vector for the process of pollination. It do not participate in the process of reproduction.
(3) Stamen Layer : It is the third layer. It takes part in the process of reproduction. Yellows colour pollen grains are formed from it which are useful in the process of fertilisation.
(4) Pistil Layer : It is the female reproductive part present in the centre of the flower. It contains ovary, style and stigma.
→ Stigma is sticky or with rough surface. It gives a place for pollen grains to stick.
Style is responsible for growing pollen tube. It connects ovary and style.
→ Ovary contains egg, which when fertilised get converted into fruit. After fertilisation egg get converted into seed.
→ The flower may be unisexual when it contains either stamen or pistil or bisexual when it contains both stamen and pistil.

→ Hydra belongs to phylum Coelenterata. Asexual reproduction is carried out in it by the process of budding
→ Here, regenerative cells are used for budding. In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site.
→ These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals.

(a) → The flower is said to be unisexual when it contains either stamen or pistil. For eg : Watermelon, papaya.
→ The flower is said to be bisexual when it contains both stamen and pistil. For eg : Hibiscus, mustard, peas.
(b) → After fertilisation sepal, petal, style, ovary shrivel and fall off.
→ Ovules gets converted into seed.
→ Ovary gets converted into fruit.
→ In some fruit, sepals are connected with the fruit.

→ Many fully differentiated organisms have the ability to give rise to new individual organisms from their body parts. That is, if the individual is somehow cut or broken up into many pieces, many of these pieces grow into separate individuals.
→ For example, simple animals like Hydra and Planaria can be cut into any number of pieces and each piece grows into a complete organism. This is known as Regeneration.

→ Regeneration is carried out by specialised cells. These cells proliferate and make large numbers of cells. From this mass of cells, different cells undergo changes to become various cell types and tissues. These changes take place in an organised sequence referred to as development.
→ However, regeneration is not the same as reproduction since most organisms would not normally depend on being cut up to be able to reproduce.

→ There are many plants in which parts like the root, stem and leaves develop into new plants under appropriate conditions.
→ This property of vegetative propagation is used in methods such as layering or grafting to grow many plants like Sugarcane, roses or grapes for agricultural purposes.
→ Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds. Such methods also make possible the propagation of plants such as banana, orange, rose and jasmine.
→ This type of vegetation loss the capacity to produce seeds.
→ Another advantage of vegetative propagation is that all plants produced are genetically similar enough to the parent plant to have all its characteristics.
→ Similarly buds produced in the notches along the leaf margin of Bryophyllum fall on the soil and develop into new plants.

→ In multicellular organisms with relatively simple body organisation, simple reproductive methods can still work. Spirogyra for example simply breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals.
→ This is not true for all multicellular organisms. They cannot simply divided cell by cell. The reason is that many multicellular organisms as we have seen are not simply a random collection of cell. Specialised cells are organised as tissues and tissues are organised into organs.
→They have been placed at definite position in the body. In such a carefully organised situation, cell by cell division would be impractical. Multi-cellular organisms therefore need to use more complex ways of reproduction.
→ A basic strategy used in multi-cellular organisms is that different cell types perform different specialised functions. Following this general pattern, reproduction in such organisms is also the function of a specific type.
→ How is reproduction achieved from a single cell type, if the organism itself consists of many cell types? The answer is that there must be a single type in the organism that is capable of growing, proliferating and making other cell types under the right circumstances.

→ The reproductive parts of angiosperms are located in the flower. We have already studied the different parts of a flower - sepals, petals, stamens and pistil. Stamens and pistil are the reproductive parts of a flower which contain the germ cell.
→ Petals and sepals protect the flower in budding stage. They do not take part in reproduction.
→ The flower may be unisexual (papaya, watermelon) when it contains either stamens or pistil or bisexual (Hibiscus, mustard) when it contains both stamen and pistil.


⇒ Stamen is the male reproductive part and it produces pollen grains that are yellowish in colour. You must have seen this yellowish powder that often sticks to our hands if we touch the stamen of a flower.
⇒ Pistil is present in the centre of a flower and is the female reproductive part. It is made of three parts.
(1) The swollen bottom part is the ovary.
(2) Middle elongated part is the style.
(3) Terminal part which may be sticky is the stigma.
⇒ Stigma is usually sticky. The ovary contains ovules and each ovule has an egg cell. The male germ-cell produced by pollen grain fuses with the female gamate present in the ovule. This fusion of the germ-cells or fertilisation gives us the zygote which is capable of growing into a new plant.

For unicellular organisms, cell division or fission leads to the creation of new individuals. Many different patterns of fission have been observed. Many bacteria and protozoa simply split into two equal halves during cell division. In organisms such as Amoeba, the splitting of the two cells during division can take place in any plane.

→ However, some unicellular organisms show somewhat more organisation of their bodies such as seen in Leishmania (which cause Kala azar), which have a whip-like structure at one end of the cell. In such organisms, binary fission occurs in a definite orientation in relation to these structures.
→ Other single - celled organisms such as the malarial parasite, Plasmodium, divide into many daughter cells simultaneously by multiple fission.