SCIENCE-CONTINUITY IN PLANT LIFE NOTES

CONTINUITY IN PLANT LIFE

NOTE: Students need to draw the diagrams related to question.

Q1: What is that characteristics of reproduction which explains the fact that a mango plant doesn’t give rise to guava or rose.

Ans:  Reproduction is the process of giving birth to new offsprings of its own kind. Here, ‘being of its own kind’ is that characteristics which explains the fact given above.

Q2: Gametes are special type of cells which take part in reproduction.

Q3: Asexual reproduction needs only one parent to give rise to new plant.

Q4: What are different modes of asexual reproduction.

Ans: Some examples of asexual  reproduction are :

a)      Vegetative propagation

b)      Spore formation

c)      Fragmentation

Q5: Spirogyra is commonly known as pond silk. It is a type of algae.

Q6: Give examples of plants in which vegetative reproduction is through following parts:

a)      Roots

b)      Tuber

c)      Bulb

d)      Runners

e)      Leaves

f)       Rhizomes

Ans: a)  Roots: Dahlia, sweet potato, Guava, Poplars, sheesham

b) Tuber: Potato

c) Bulb: Onion, cactus, lily

d) Runners: grass, strawberry

e) Leaves: Bryophyllum

f) Rhizomes: Ginger, canna, turmeric

Q7: Potato tubers have buds or eyes which give rise to new plant.

Q8: What is the difference between rhizomes and Stolon(runners)?

Ans: A runner is a horizontal connnection between organisms. In plants, these are stems that grow at the soil surface or just below, and are also known as runner. We can see these in weeds, strawberries,  grasses, lily of the valley and others and it is a propagation strategy allowing plants to spread out from one main plant and survive during times that are not so advantageous until the next season. A stolon sprouts from an existing stem.

A rhizome is a root-like stem, which is the main stem, that can grow horizontally or other directions underground. A rhizome is the stem of a plant underground that sends out roots and shoots from its nodes.  An example is a ginger plant, an iris, canna lily, and others. When using vegetative propagation, the rhizomes can be separated and new plants will grow.

Q9: How does bryophyllum leaf show propagation?

Ans: A Bryophyllum leaf has tiny leaves along the margin known as buds. These buds along the margins get detached from the main leaf and grow into new plant. Chinese tea flower and African violets are similar example of plant that can be grown from leaf cuttings.

Q10: Explain artificial methods of vegetative methods of reproduction.

Ans: Following are the methods of artificial vegetative reproduction:

1

.      Cutting: new plants are obtained by replanting the cut stem or leaf of the parent plant. E.g. rose, hibiscus and money plant.

2.      Grafting: In this method a bud or shoot is cut from one plant which has good leaves, fruit or flowers and inserted into a cleft or under the bark on the stem of a closely related plant variety with good roots. The former is called as graft or scion and the later stock.  

3.      Layering: In this method, the lower branch of the plant is arched to the ground, held in place and covered with moist soil. After some time, roots start growing from the covered part which is then separated from the parent plant. E.g. rose, jasmine, grapevine.

4.      Tissue culture: Many plant cells have the ability to regenerate a whole plant when supplied with appropriate nutrients and hormones. Plants are propagated under controlled conditions and exact replicas of plant are produced.

Q11: Draw the structure of flower and explain its different parts.

Ans: A typical flower has four parts-sepals, petals, stamens and carpel

Petals: are brightly coloured and scented parts which together are called corolla. It attract insects and birds and protect the inner delicate parts of the flower.

Sepals: are small leaf-like structures at the base of the flower. Their main function is to protect the flower at the bud stage. Sepals together are called calyx.

Stamen: male part. It consists of a stalk or a filament and knobbed sac like tip called anther. Anther produces pollen grains.

Pistil: female part. It is made up of carpel or many carpels. Carpel is made up of three parts –stigma, style and ovary.

Q12: What is the difference between bisexual and unisexual flower.

Ans: Bisexual flowers: Flowers having male and female reproductive part is called a bisexual flower such as lilies, gulmohar, roses, hibiscuses and sweet peas.

Unisexual flowers: A flower having either male or female reproductive part is called a unisexual  flower. E.g  pumpkin, papaya, watermelon, bittergourd and corn.

Q13: Why do you think some plants have brightly coloured flowers?

Ans: The brightly coloured flowers attract the insects and birds, which aid in polination.

Whereas plants that have light coloured flowers, either self pollinate or have other means of pollination like, wind or water)

Q14:  How do you think aquatic plants pollinate?

Ans: They release the pollens in the water and with the water currents these pollens reach to distant places. E.g. Vallisneria

Q15: What is fertilization and its zygote.

Ans: The male gamete from the pollen grain fuses with the female gamete (egg cell) in the ovary. This process is called as fertilization.  A zygote is formed as a result of fertilization.

Q16: Which insect is responsible for most pollination?

Ans: Honeybees account for the 80% of insect pollination that take place. For example apple, mango, beet and onion are pollinated by bees.

Q17: Define some important terms:

a)      Ovule- the part of the ovary of seed plants that contains the female germ cell and after fertilization becomes the seed.

b)       Gametes- a mature male or female germ cell which is able to unite with another of the opposite sex in sexual reproduction to form a zygote.

c)       Zygote- A zygote is a single cell formed as a result of fusion of a male gamete with the female gamete.

d)       Fertilization- the action or process of fertilizing an egg or a female plant, involving the fusion of male and female gametes to form a zygote.

Q18: Explain the formation of seed and then fruit.

Ans: As the zygote is formed, the wall of ovary becomes the fruit wall and the ovules become the seeds. Depending on the ovules in the ovary the number of seeds may vary in a fruit.  Conifers do not have ovary and therefore the seeds are not enclosed in any kind of fruit.

Q19: Draw structure of a seed and brief about its parts.

Ans: The seed has following parts:

a)      Seed coat: The outer covering of the seed is called seed coat. It has a tiny pore called micropyle. Water and oxygen enter through this pore during germination.

b)      Cotyledons: It stores food material which the baby plant utilizes for its growth.

c)      Embryo: is protected by the seed coat and cotyledons. It eventually develops into a new plant.

Q20: What is radicle and plumule?

Ans: An embryo has two parts: radicle and plumule. During germination, radicle develops into root system whereas the plumule develops into shoot system.