All single celled organisms are placed under the Kingdom Protista or Protoctista. The term Protista was first used by Ernst Haeckel in the year 1886. This kingdom forms a link between other kingdoms of plants, animals and fungi. Protists represent an important step in early evolution. The first protists evolved probably 1.7 billion years ago. Members of Protista are primarily aquatic in nature. It is a very large group comprising of at least 16 phyla. Many protists like algae are the primary producers in the aquatic ecosystem, some protists are responsible for serious human diseases like malaria and sleeping sickness.
Structure and Reproduction of Chlorella
Chlorella is green alga. It grows in fresh water places, such as ponds, ditches and pools etc.Chlorella is unicellular or found in groups. The cells are small and spherical. Each cell is covered by a thin cell wall, composed of cellulose. In the cell cytoplasm is present. In the centre of cell nucleus is present. Each cell also contains a cup-shaped chloroplast. In the chloroplast pyrenoid is sometimes present or sometimes absent. Pyrenoid is a starch-forming body. In chlorella flagella are absent i.e. it is non-motile.
Chlorella has only asexual reproduction. It takes place by aplanospores. At the time of reproduction the cytoplasm of cell divides into 8 or 16 small bodies. Each body is covered by a wall, it is called aplanospore. In this way 8 or 16 aplanospores are formed in a cell. After maturation of aplanospores the cell wall ruptures and all aplanospores become free. Each aplanospore can develop into a new cell.
Economic Importance of Chlorella
- Chlorella cells have very high food value. They contain about 50% proteins, 20% carbohydrates and 20% fats, amino acids and vitamins, so it can be an alternate source of food.
- From chlorella an important antibiotic chlorellin has been isolated. It is useful to control bacterial diseases.
- Chlorella is used in important physiological experiments. Because it is easily cultivated. It is used in the research on photosynthesis and respiration.
Structure of Ulva:
Ulva belongs to the green algae. It grows in marine water and is considered as a primitive plant in the group. It is also known as sea-letuce. It’s body is called thallus which consists of erect broad sheet-like branches, or blades. From the base of plant thread like colourless structures are given out which help in the attachment of plant to any rock or stone and thus act like a hold-fast. The hold fast does not absorb water. The body of Ulva is composed of two layers of cells. The outer layer has contact with water, while the inner layer is prevented from the water contact. The cells are elongated. Each cell contains cytoplasm, a nucleus and a single cup-shaped chloroplast.
Life Cycle of Ulva:
The life cycle of Ulva is completed in two stages. The first stage is gametophyte, in which the male and female gametes are produced by separate plants. These gametes unite together to form zygote. The zygote develops into sporophyte, which is the second stage of life cycle. The sporophyte forms spores which produce gametophyte again. This whole process of life cycle is called alternation of generations. In Ulva gametophyte and sporophyte plants are similar in structure, so this process is termed as isomorphic alternation of generations. The life cycle is described as follows:
- Gametophytic Stage
In this stage sexual reproduction takes place and two types of male and female gametes are formed. The male and female plants are separate but similar in structure. The male plant produces male gametes and female plant produces female gametes. These male and female gametes are externally similar and internally different, they are called isogametes. They come in water and fuse together to form zygote. The zygote is diploid and it contains 26 chromosomes. It germinates into sporophyte which is also diploid in nature.
- Sporophytic Stage
It is the second stage of the life cycle of Ulva. It is developed by the germination of zygote. The sporophyte resembles to gametophyte in structure. The sporophyte produces zoospores by asexual reproduction. In the formation of zoospores meiosis takes place due to which they become haploid and contains 13 chromosomes. The zoospores become free after maturation. Half of the zoospores form male and half produce female gametophyte of Ulva plant. In this way it’s life cycle is completed.
Structure of Slime Mold
Slime mold are creeping multinucleate masses of cytoplasm, look like egg white. The body of slime mold consists of irregularly shaped mass of protoplasm, which is naked i.e. has no proper body wall. The naked protoplasm is bounded by a non-cellular, thin flexible slimy layer. Due to the presence of slime layer it is called slime mold. Within the slime layer protoplasm also contains plasma membrane. Slime mold has no proper shape and size. The protoplasm consists of outer ectoplasm and inner endoplasm. The protoplasm contains many diploid nuclei. This body of slime mold is called plasmodium. It produces pseudopodia and shows amoeboid movement, so it seems to be like a gaint amoeba. By the help of pseudopodia it engulfs and digest bacteria and food particles, so it also contains food vacuoles and undigested food particles in the cytoplasm.
Classes of Phylum Protozoa
The phylum protozoa is divided into following classes:
- Class – Mastigophora – Flagellata
- Class – Rhizopoda or Sarcodina
- They have very soft body wall, which can change the shape of the body. In some animals the body is covered by a shell. E.g. Globigerina.
- From their outer surface pseudopodia are produced which help in locomotion and to capture the food.
- The protoplasm is divided into ectoplasm and endoplasm.
- Nucleus is one or more.
- Excretion takes place by contractile-vacuole. In marine animals contractile vacuole is absent.
- Class – Ciliata
- Their body is provided by cilia, which help in locomotion and to get food into the body.
- They have mouth, through which the food enters the body. The food may also be taken through the general surface.
- They contain two nuclei, micronucleus and meganucleus.
- Body is covered by pellicle.
- Excretion takes place by contractile vacuole.
- Class – Suctoria
These animals have close relationship with Ciliata animals and they seem to be evolved from them. Their characters are as follows
- They have cilia which help in swimming but the adult animals are without cilia.They are attached to any solid object by the help of a long rod-like structure.
- They contain two types of nuclei, micronucleus (smaller) and meganucleus (large).
- From their body certain thin structures are developed, called tentacles. Some tentacles are pointed and penetrate into the body of prey. Some tentacles have knob-like bodies at their tips which help to capture the prey. Tentacles secrete a poisonous substance to paralyse the prey.
- Reproduction takes place by budding e.g Acinata.
- Class – Sporozoa
- The animals of this class are usually parasites.
- They do not produce special organs for locomotion. They perform very slow movement, called amoeboid movement.
- They contain cytoplasm and nucleus.
- Reproduction takes place by asexual sexual methods.
- They cause some dangerous diseases in man and other vertebrates such as malaria by plasmodium.
- Their life cycle is completed in the body of two hosts. One is the body of vertebrate and other is the body of invertebrate. The plasmodium is transferred into the body of man from the body of female anopheles mosquito.
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These are the practice tests included in Kingdom Protista