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title. Reproduction (I). Reproduction. the process of producing offspring. necessary for the continuation of a species. Two types of reproduction. Reproduction. Asexual. Sexual. Two types of reproduction. Reproduction. Asexual. Sexual. usually involves 2 parents involves gametes
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title Reproduction (I)
Reproduction • the process of producing offspring • necessary for the continuation of a species
Two types of reproduction Reproduction Asexual Sexual
Two types of reproduction Reproduction Asexual Sexual • usually involves 2 parents • involves gametes • involves fertilization • fusion of the nuclei of male & female gametes zygote • offspring are genetically different from each of their parents • involves one parent • involves no gamete (sex cell) • offspring are genetically identical to the parents – mitotic cell division
Types of asexual reproduction Examples of asexual reproduction Binary fission Budding Spore formation Fragmentation Vegetative propagation
Binary fission Binary fission • division of unicellular organisms into equal halves • e.g. Amoeba
Binary fission nucleus divides equally into two by mitosis nucleus Amoeba rounds up cytoplasm constricts a fully grown Amoeba two daughter Amoebae are formed
Budding • production of buds, which grow to new individuals • e.g. yeast
Budding a nucleus moves into the bud a bud is formed nucleus vacuole a yeast cell a nucleus remains in the parent cell nucleus divides into two
Budding the new cell breaks off from the parent cell a new cell is formed from the bud before the bud breaks off from the parent cell
Spore formation • production of spores which develop into new individuals under favourable conditions • spores produced in large numbers to increase the chance of reproduction • occurs in fungi • e.g. Mucor, Rhizopus
Spore formation Fungal spores of penicillium
Fragmentation Amazing power of regeneration in starfish
Fragmentation regeneration in flatworm
Vegetative propagation Vegetative propagation • development of new plants from vegetative / food storage organs • occurs in flowering plants • e.g. potato, onion, ginger, Gladiolus
Vegetative propagation bud storage organ aerial parts • When conditions become unfavourable such as winter, the aerial parts of the plant die and the storage organ stops growing underground. It survives through bad conditions for growth.
Vegetative propagation • When conditions are suitable for growth, a new plant develops from a bud. The storage organ provides food for the development of the new plant.
Vegetative propagation • Adventitious roots are formed. They absorb water and minerals. aerial shoot The shoot grows up and develops leaves. adventitious roots
Vegetative propagation leaf • The storage organ dries up as food is used up for growth.
Vegetative propagation • The plant can now survive on its own by food made from photosynthesis. new storage organ Some food made from photosynthesis is passed to a new storage organ. previous storage organ
Vegetative propagation Examples of storage organs Tuber Bulb Rhizome Corm • short underground stem with layers of fleshy ‘scale leaves’ • e.g. onion bulb • horizontally growing underground stem • e.g. ginger • rhizome • swollen underground stem • e.g. potato • tuber • short swollen underground stem • e.g. Gladiolus • corm
Vegetative propagation Tuber Vegetative propagation of a potato plant In spring In winter • Each bud can produce a new independent plant. • The aerial shoots die but the new tubers remain dormant.
shoot tuber formed by last year’s plant In summer old tuber new tubers adventitious roots eye (a bud) • Excess food made in the leaves is sent to the underground shoots and stored. • The buds use the food stored in the tuber to produce adventitious roots and shoots.
Vegetative propagation Bulb an onion bulb
Vegetative propagation Bulb Growth of an onion bulb scale leaf fleshy leaf bud • The bud remains dormant.
new flower stalk leaf fleshy leaf new bulb • After dormancy, the bud develops. • The leaves make and provide food for the growth of a new bud. The fleshy leaves provide food for the development of the shoot. They become dry scale leaves after their food storage has been used up.
Vegetative propagation Rhizome Growth of a ginger rhizome In spring In summer aerial shoot lateral bud grows into daughter rhizome lateral bud grows to form underground branches leaf lateral bud behind the leaves • The food produced from photosynthesis passes downwards to the underground parts. • Food passes upwards from the older parts to the growing regions.
Vegetative propagation Corm Growth of a Gladiolus corm In spring bud scale leaf remains of last year’s corm • Food stored in the swollen stem is passed upwards to the bud for its growth.
aerial shoot leaf new corm new corm old corm • A new corm is developed over the old one each year. • When the leaves are well developed, the food they made is passed down to the new corm.
Vegetative propagation Artificial vegetative propagation • vegetative propagation done artificially • can produce desired varieties quickly • method: taking of ‘cuttings’ • e.g. Coleus (stem), • African violet (leaves)
Importance of Vegetative Propagation • It is the only means of reproduction for seedless plants such as pineapples, seedless grapes, oranges, roses, sugarcane, potato, banana, etc. • Plants raised through vegetative propagation are genetically similar. It preserves the type of characters that a plant breeder desires to retain. • It is very economical and easy method for the multiplication of plants.
Artificial propagation by grafting Eg. Fruit trees Ornamental plants Bauhinia of HK Grafting is a method of asexualplant propagation where the tissues of one plant are encouraged to fuse with those of another. In most cases, one plant is selected for its roots, and this is called the stock or rootstock. The other plant is selected for its stems, leaves, flowers, or fruits and is called the scion.
Artificial Vegetative reproduction • To ensure a quick growth union, all cut surfaces are covered with a soft wax to prevent drying. The tissues of both the stock and the scion will fuse together and will make organic connection, getting nourishment from the stock, but producing fruits of scion retaining parental characters. Grafting is not possible is monocot plants since cambial activity is essential for the union of stocks and scion. • Grafting blends the properties of two plants. It is also used in the production of dwarf fruit trees for the home gardens. High quality roses are usually grafted on wild rose root stocks. Other plants where grafting has been performed successfully are rubber, apple, pear, mango and guava.
Grafting peach into plum Main grafting steps: Trimming bark after cutting a branch to be grafted Next: Budwood inserted into branch Completed bark graft which has been tied with tape and waxed with grafting wax These peach grafts were been successful and have already produced blossoms This wild plum tree has now become half peach and half plum
The ‘grafted’ Bauhinia appear in two segments: the upper half is Bauhinia blakeana 洋紫荊and the lower half is Bauhinia purpurea 紅花羊蹄甲. When you look at the joint carefully, then you will notice that the bark textures on both halves are significantly different. Also, the leaves on the branches and those near the foot vary a little bit. When we see the ‘grafted’ Bauhinia, Bauhinia blakeana is just one of the tree names. Bauhinia purpurea is another one. (Well, if the foot of this tree does have leaves and flowers, then it should be labeled with two names!)
What are the ADVANTAGES and DISADVANTAGES of Artificial Propagation ?
Vegetative propagation Disadvantages Advantages Speed? Good characters? External agents?
Vegetative propagation Disadvantages Advantages Overcrowding….. A relatively quick way to produce new plants Good characters are passed to the offspring Diseases in parents….. Offspring are identical….. No external agents or other plants are needed Undesirable characters….
Vegetative propagation Disadvantages Advantages Overcrowding can occur which causes competition for resources A relatively quick way to produce new plants Disease of the parent plants can easily be transmitted to the offspring Good characters of the parent are passed to the offspring Offspring have no new features No new features in offspring to adapt to any changes in environmental conditions No external factors or other plants are needed for reproduction Undesirable characters are passed on to the offspring
