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Classification of kingdom Protista: Plant-Like Protists (Chrysophyta, Pyrrophyta, Euglenophyta), Practice Problems and FAQs

Classification of kingdom Protista: Plant-Like Protists (Chrysophyta, Pyrrophyta, Euglenophyta), Practice Problems and FAQs

Have you ever seen the ocean light up? If not in person, maybe in the movies. It is an extremely beautiful phenomenon to watch. You must be wondering, how does the ocean light up? Right? You will be amazed to know that these lights are produced by some kind of organisms, which are classified as Protists (unicellular eukaryotes) in the five kingdom classification. 

Do all protists produce such lights? No, they do not. This special characteristic is exhibited only by some groups of photosynthetic protists which are commonly called as plant-like protists. Come let us learn more about them.

Table of contents

  • Plant-like protists
  • Practice problems
  • Frequently Asked Questions

Plant-like protists 

Protists are classified into three main categories depending on the similarities to plants, fungi and animals. They are plant-like protists, fungi-like protists and animal-like protists. Here we are going to discuss more about plant-like protists.

Plant-like protists are photosynthetic in nature and are further classified into Chrysophyta, Pyrrophyta and Euglenophyta.


This group is also called golden algae because of its golden colour. They are found in fresh water as well as in marine environments and can float passively in water currents. Most of them contain photosynthetic pigments and can prepare food by photosynthesis. The cells are diploid in nature. This group includes diatoms and desmids.

Fig: Golden algae


These are photosynthetic, unicellular organisms which are also known as the ‘Jewels of the Plant Kingdom’. These serve as the chief producers of the marine ecosystems. The cell wall of diatoms is made up of cellulose and is impregnated with silica which makes them indestructible. Their cell wall is made up of two shells or frustules which are arranged like lids of a soap box. Deposits of dead diatoms form diatomaceous earth which is used in filtration of oils and syrups, polishing metals, insulating refrigerators, etc. Reproduction in diatoms is mainly asexual. Sexual reproduction is rare.

Fig: Diatoms - Jewels of the Plant Kingdom


Desmids are unicellular, microscopic organisms. Desmids have pigments chlorophyll a, chlorophyll b and xanthophyll (fucoxanthin) due to which they appear golden coloured. Their body is divided into two halves which are connected by an isthmus. Food in these organisms is stored in the form of oil droplets.

Fig: Desmids


They are microscopic unicellular organisms commonly called dinoflagellates. Because they have two flagella beating in different directions. So they are motile and flagellated.

They are mainly marine and are found on the surface of water. Depending on the main pigments present in the cells, dinoflagellates may appear yellow, green, brown, blue or red. In Dinoflagellates, the nutrition is mainly holophytic (photosynthetic). Their cell wall is formed of plates made up of cellulose. They have two flagella, one transverse and the other longitudinal between the cell wall plates. 

Fig: Two flagella in Dinoflagellates

GIF: Flagella in dinoflagellates

A large nucleus named mesokaryon is present in them. Reproduction is mainly asexual. Sexual reproduction is very rare and can be isogamous or anisogamous. Dinoflagellates such as Noctiluca (night light) and Gonyaulax show bioluminescence.

Fig: Noctiluca (Night Light)

Red dinoflagellates such as Gonyaulax spreads on the surface of sea water, through rapid multiplication due to which sea water appears red. It is called red tide. These dinoflagellates also release toxins (dinophysis) into water bodies which adversely affect marine life. Examples: Noctiluca, Ceratium, Gonlyaulax, Gymnodinium.

Fig: Red tide


They are commonly called Euglenoids. They are unicellular and microscopic. They are generally found as free living organisms in freshwater lakes, ponds etc. but sometimes can also be present in damp soil and brackish water. They are single-celled and do not possess a cell wall. The cell membrane is surrounded by a protein rich pellicle which provides flexibility.

Fig: Structure of Euglena

The organisms have two unequal flagella, a long one and a short one, which arise from the blepharoplast. Locomotion is hence flagellar. One eye spot is present at the anterior position which serves as a photoreceptor. They have a contractile vacuole which helps in osmoregulation. Euglenoids have a haploid nucleus. Being photosynthetic, euglenoids have chlorophyll a, b, xanthophyll and carotenoid pigments in chloroplasts. These organisms are mixotrophic. They photosynthesise in presence of sunlight but become heterotrophic predators in its absence. Examples: Euglena and Paranema.

Fig: Euglena

Practice Problems

Q1. Match the columns.music


Column I


Column II


















Solution: The diatoms belong to the group Chrysophytes which include the golden algae.Gonyaulax is a dinoflagellate and it causes the ‘red tide’ phenomenon. Euglena is a photosynthetic protist, belonging to the euglenoids, is considered to be the connecting link between plants and animals as it has characteristics of both. Paramoecium is a ciliated protozoan and is commonly called the ‘slipper animalcule’ because of its shape.

Hence the correct option is a

Q2. Given below is an assertion and reason.

Assertion: Euglena has chlorophyll, a feature similar to plants.

Reason: Euglena cannot be classified on the basis of two kingdom classification. 

Find the correct statement.

A. Both assertion and reason are true and reason is the correct explanation
B. Both assertion and reason are true but reason is not the correct explanation
C. Assertion is true, but reason is wrong
D. Both assertion and reason are wrong

a. A
b. B
c. C
d. D

Solution: The animal-like characteristics of Euglena include - lack of cell wall, presence of contractile vacuole, a flagellum and a light sensitive eyespot. Plant-like characteristics include presence of chlorophyll and the ability to photosynthesise. It cannot be classified in the two kingdom classification due to these reasons. Thus, Euglena has been kept under Kingdom Protista in Five Kingdom Classification. 

Hence the correct option is b.

Q3. Why do marine protozoa do not have contractile vacuole?

A. Their body cannot accommodate it
B. They are hypo-osmotic to their environment
C. They are isotonic to their environment
D. Osmoregulation is done by the cell membrane

Solution: Contractile vacuole helps to remove excess water and thus performs osmoregulation. It is helpful for organisms living in hypotonic conditions such as ponds where the surrounding solution has less solute than the fluids inside the cell. The marine protozoans are hypoosmotic or hyptonic to their environment. When one solution has a lower osmotic concentration than another, it is said to be hypoosmotic. As marine protozoans live in a hypertonic environment which has less water and more solute compared to their body, they lose water due to exosmosis. Thus, they lack a contractile vacuole in order to prevent water loss and conserve water in the body.

Hence the correct option is b.

Q4. Unlike other protists, diatoms do not easily decay due to:

A. Siliceous wall
B. Mucilaginous wall
C. Waterproof cell wall
D. Calcareous wall

Solution: Diatoms have a structure similar to an overlapping soap box and the cell wall is made up of silica. The siliceous wall is indestructible so diatoms do not readily decay even after their death. The cell wall of diatoms has two layers. The inner layer is made up of pectin-like material enclosing the protoplast and the outer layer is made up of silica. The cell wall contains two halves which overlap and is fixed together. Silica does not decompose easily so it preserves the diatom for a long period of time without decay resulting in the formation of diatomaceous earth or kieselguhr.

Hence the correct option is a.


Q1. Which of the protista is used in the manufacture of toothpastes?
Answers: Diatoms are white, soft, and porous in nature, and when they die, they leave behind organic compounds and silica-based shells. Diatom-derived silica is used in tooth powder and toothpaste because of its moderate abrasive properties.

Q2. Can red tide cause any negative impact on humans?
Answer: Red tide can cause serious sickness in persons who have severe or chronic respiratory disorders like emphysema or asthma. Toxins from red tide can build up in molluscan filter-feeders like oysters and clams, causing Neurotoxic Shellfish Poisoning in people who eat contaminated shellfish.

Q3. What is the economic importance of euglena?
Answer: Euglena can be used in the five domains of food, fibre, feed, fertiliser, and fuel, together known as the 5 "F's of the Biomass Model. As food, Euglena helps to alleviate malnutrition by providing sufficient nourishment and being conveniently transportable in powder form to impoverished countries. Euglena can be used as a healthier dietary option in industrialised countries to combat diabetes and obesity. Euglena has the potential to be used in innovative paramylon-based fibre composites. Paramylon has been proved in studies to be an effective fibre material with unique features such as wound healing. Euglena can be used as a feed for cattle and aquafarm fish due to its high protein and nutritional content. It can also be used as a fertiliser. Euglena feed may reduce young fish mortality, and the leftovers from Euglena after biofuel extraction can be used as feed and fertiliser, which helps to reduce waste. In the field of Euglena as fuel several research and development projects are carrying on to generate microalgae-based biofuels. By 2020, Euglena Co., Ltd. intends to have a functional aircraft biofuel.

Q4. What is the purpose of bioluminescence?
Answer: While not all animals utilise bioluminescence for the same reasons, it is commonly employed to warn or evade predators, to entice or find prey, and to communicate amongst members of the same species.


Related Topics

Kingdom Protista: Overview 

Classification of Kingdom Protista: Fungi-like protists, Animal-like protists 

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