Protists and fungi

7.1Protists: the evolutionary relationship

Protists are a diverse group of mainly aquatic organisms. They differ in shape, in the way they feed and reproduce, and in their way of life, so they are hard to classify. Biologists believe there may be up to 200,000 protist species. Each one is either single-celled or a simple multicellular organism, and every one has eukaryotic cells.

Protist

A eukaryotic organism that is not a fungus, an animal or a plant. The name comes from a Greek word meaning "the very first", because protists were among the first eukaryotes to evolve. Protists are defined mainly by what they are not, because they do not fit into the categories of plants, animals or fungi.

Polyphyletic

A grouping of organisms that do not share a common evolutionary ancestor. Its members may have evolved independently from different ancestral sources and are not closely related in their evolutionary history.

All protists have eukaryotic cells, like those of fungi, animals and plants. This is what sets them apart from bacteria, which are prokaryotes. Eukaryotic cells have a nucleus and other parts enclosed in membranes, such as mitochondria and plastids.

Biologists differ on what exactly protists are. Some think of the protist kingdom broadly, including both the heterotrophs (protozoa, slime molds and water molds) and the autotrophs (algae).

Polyphyletic origin: where protists come from

Protists do not all come from the same ancestor. They have many different origins. Any eukaryotic organism that is not a fungus, an animal or a plant is put into the protist category just for convenience. If protists were sorted by more specific shared characteristics, there might be many categories within Protista, perhaps as many as twenty.

The remarkable diversity of protists

Coenocytic

Having many nuclei in one continuous cell, with no cross-walls between them.

Symbiosis

Two organisms living in association: mutualism (both benefit fairly equally) or parasitism (one organism depends on the other for its metabolic needs, living on or inside it).

Extremophile

A protist that lives in an extreme environment such as snow, hot springs or acidic ponds.

7.2Major groups of protists

Protists can be classified into several groups based on their characteristics and their evolutionary relationships. The book describes four major groups: protozoa, algae, Myxomycota and Oomycota. Their salient features are discussed in the following sections.

Salient features

The primary and easily recognisable characteristics or attributes of something: the key points that define it.

7.2.1Protozoa: the animal-like protistsOften examined

The term protozoa is derived from two Greek words: "proto", meaning "first", and "zoa", meaning "animals". It was coined in the 19th century to describe microscopic, single-celled organisms that showed animal-like behaviours, such as movement and ingestion of food particles. Protozoa are a polyphyletic group.

Habitats

• Fresh water: Amoeba and Paramecium.
• Marine ecosystems: Radiolaria.
• Parasites: Plasmodium and Entamoeba histolytica.
• Soil, leaf litter and decaying organic matter: Spiromonas and Vorticella.

Structure and life activities

Protozoa are unicellular. The body is a single mass of cytoplasm that holds all the structures found in a typical cell. Protozoa do everything that living things do: they eat, breathe, move, maintain fairly stable conditions (homeostasis) and reproduce.

Vacuoles

Present in protozoa to perform specialised functions.

Food vacuole

Helps digestion by breaking down trapped food into simpler molecules with the help of enzymes.

Contractile vacuole

Found in many freshwater protozoa. It regulates the water content of the cell by pumping excess water out of the cell, and so maintains the internal balance.

Storage vacuole

Stores waste products, nutrients or other substances that the cell needs to keep separate from the rest of its cytoplasm.

Some protozoans have a shell, for example foraminifera.

Reproduction, locomotion and survival

• Reproduction takes place by both asexual and sexual methods.
• The organs of locomotion may be pseudopodia (Amoeba), cilia (Paramecium) or flagella (Trypanosoma). Parasitic protozoans such as Plasmodium (the malarial parasite) have no specific means of locomotion.
• Regeneration is common in protozoans.
• Protozoans form resistant cysts to overcome unfavourable conditions.

Amoebas

Amoebas are free-living microorganisms inhabiting fresh water, oceans and soil, and some live as parasites inside animals. Amoebas use pseudopodia for both movement and feeding, as in Amoeba proteus and Entamoeba histolytica (Figure 7.1).

Zooflagellates

Protozoa that move using flagella are called zooflagellates. An example is Giardia intestinalis (Figure 7.2a), a flagellated parasite that infects the small intestine and causes a gastrointestinal illness known as giardiasis in humans.

Choanoflagellates

A choanoflagellate is a marine or fresh-water flagellate that is sessile and remains anchored in place by a stalk. It has a flagellum surrounded by a delicate collar, resembling the collar cells found in sponges (Figure 7.2b).

Ciliates

Ciliates are named after a Latin word for "eyelash", which fits because their cells are covered in tiny hair-like structures called cilia. Examples of ciliates include Paramecium, Stentor and Vorticella (Figure 7.3).

Foraminifera and actinopods

These are often called forams: marine protozoa that create protective shells or tests. In foraminifera (Figure 7.4 a, b) the shells are composed of calcium, while in actinopods the shells are made of silica (Figure 7.4 c, d).

Apicomplexans

Apicomplexans are a large group of parasitic protozoa known for their complex life cycles and specialised structures used for host-cell invasion. Some cause diseases in humans, for example Plasmodium, the malarial parasite.

7.2.2Algae: the plant-like protistsOften examined

Algae (singular: alga) are organisms found in various environments: oceans, fresh-water ponds, lakes, streams, hot springs, polar ice, moist soil, trees and rocks. They play a vital role in ecosystems and are responsible for about 50 to 60% of photosynthesis on our planet.

General characteristics of algae

• Algae come in different shapes and sizes. Some are unicellular, while others form long filamentous structures or even multicellular bodies.
• In filamentous algae the multicellular structures lack cross-walls and individual cells, a feature known as coenocytes.
• In multicellular algae such as seaweeds the body takes on a branched or leaf-like form called a thallus.
• Unlike higher plants, algae do not have roots, stems, leaves or vascular tissues.
• Algae have a vibrant collection of photosynthetic pigments: chlorophyll "a", and yellow and orange carotenoids, xanthophyll and phycoerythrin. These enable them to harness energy from sunlight and convert it into food.
• Algal life cycles show remarkable diversity. Almost all algae, except red algae (phylum Rhodophyta), have stages in their life cycle with flagellated motile cells that move by whip-like flagella.
• Algae differ from plants in that they have unicellular sex organs, their zygotes are not protected by the parent organism, and they do not form embryos like plants.

Coenocyte

A unique structure found in some filamentous algae in which multiple nuclei coexist within a single, continuous cell. Unlike a typical cell with one nucleus, a coenocyte has many nuclei within a shared cytoplasm, so it can perform various functions at the same time. This adaptation improves the efficiency of processes such as nutrient uptake and growth.

Thallus

The branched or leaf-like body of a multicellular alga such as a seaweed.

Algae are classified into six phyla, each with its unique features: euglenoids, dinoflagellates, diatoms, brown algae, red algae and green algae.

Euglenoids

Euglenoids are tiny fresh-water organisms that show plant-like pigments. Approximately one-third of the genera possess chloroplasts, while the remaining two-thirds lack them. Those without chloroplasts obtain food through ingestion or absorption. Euglena is a common example (Figure 7.5).

Dinoflagellates

Many dinoflagellates are bounded by protective cellulose plates impregnated with silica. Most have two flagella. They vary in colour from yellow and green to brown (Figure 7.6).

Diatoms

Diatoms (Figure 7.7) are the most numerous unicellular algae in the oceans. They are also plentiful in fresh water. The structure of a diatom is often compared to a box, because the cell wall has two halves, with the larger half acting as a "lid" for the smaller half.

Brown algae

Brown algae come in various sizes, from small types with simple filaments to massive multicellular forms reaching lengths of up to 75 m. They grow well in cooler marine environments. The massive brown algae are commonly known as kelps (Figure 7.8, Laminaria).

Red algae

Red algae are multicellular organisms found mainly in warm seawater, growing in both shallow and deep regions. They can grow up to a metre in length and are anchored to rocks or other surfaces by a base called a holdfast (Figure 7.9).

7.2.3Green algae

Green algae are tiny plants that live in water. They are believed to be closely related to the first plants, because both groups have a cell wall that contains cellulose and possess chlorophyll a and b. They are important because they make oxygen and use sunlight to grow.

These algae come in many shapes and sizes and can live in diverse aquatic environments, and can even be found on land. Some are microscopic and not visible with the naked eye, while others are bigger. Common examples are Chlamydomonas, Spirogyra, Volvox, Chlorella and Ulva.

7.2.4Fungus-like protists: Myxomycota (slime molds)Often examined

The fungus-like protists are the Myxomycota (slime molds) and the Oomycota (water molds). Slime molds, specifically plasmodial slime molds, typically exist as a plasmodium.

Plasmodium (of a slime mold)

A diploid, multinucleated cytoplasmic mass wrapped in a slime sheath.

Sporangium

(Greek spora: seed, and angeion: vessel) a reproductive structure that produces spores by meiosis.

Under unfavourable conditions for growth, for example when there is not enough water, the plasmodium develops many sporangia. These sporangia make new cells called spores through meiosis. In plasmodial slime molds the spores release a haploid flagellated cell or an amoeboid cell. Eventually two of these cells fuse to form a diploid zygote, which feeds and grows, producing a multinucleated plasmodium once again.

Slime molds interest biologists because the life cycle involves many changes in form. These different forms resemble other types of protists.

7.2.5Oomycota: the water moldsOften examined

Oomycetes include water molds, white rusts and downy mildews. They are typically found in aquatic environments or moist terrestrial ones. The members of the group are either parasites or saprotrophs. Some are parasites of plants, while a few aquatic oomycetes are animal parasites.

Saprotroph (saprophyte or saprobe)

An organism that feeds on non-living and rotten organic matter known as detritus at a microscopic level.

• The cell wall of oomycetes contains cellulose, unlike fungi, which have chitin.
• They have filamentous structures called hyphae, as in fungi. The hyphae are aseptate, that is, without intercellular cell walls, and are coenocytic.

Life cycle of oomycetes

The life cycle is characterised by both sexual and asexual reproduction.

• Asexual: swimming spores called zoospores are produced from structures called sporangia. Zoospores are released into the environment and move through water by means of a single, whip-like flagellum. They find suitable conditions to attach, germinate into germ tubes and form filamentous hyphae.
• Survival: some oomycetes also produce thick-walled oospores, which serve as a survival strategy.
• Sexual: there are two types of gametangia. The female gametangium is the oogonium and the male gametangium is the antheridium. The antheridia contain numerous male nuclei, which are functional male gametes. The oogonia contain from one to eight eggs, which are female gametes.

The contents of an antheridium move into an oogonium, and one or more pairs of male nuclei fuse with eggs. The cell wall around the resulting zygote or zygotes then thickens. This produces a special kind of thick-walled cell called an oospore, which gives the phylum its name (Oomycota). Common examples of oomycetes are Phytophthora infestans and Saprolegnia.

Zoospore

A swimming spore with a single whip-like flagellum, produced asexually in a sporangium.

Oogonium

The female gametangium, containing one to eight eggs.

Antheridium

The male gametangium, containing numerous male nuclei that act as gametes.

Oospore

The thick-walled zygote that survives unfavourable conditions; it gives the phylum its name.

7.2.6Importance of protists to humansOften examined

Protists are a diverse group that has both useful and harmful impacts on humans.

Paralytic shellfish poisoning

Dinoflagellates of the genus Alexandrium produce a neurotoxin. The toxins accumulate in shellfish when the shellfish feed on these dinoflagellates. When humans eat the contaminated shellfish, the toxins can cause paralysis by blocking the transmission of nerve signals to muscles. The paralysis can extend to the respiratory muscles and may lead to respiratory failure if left untreated.

Potato blight caused by Phytophthora infestans

Potato plants infected with Phytophthora infestans show individual leaflets with small brown, dead and scarred areas. Short specialised branches called haustoria penetrate the leaves to obtain nourishment. In addition to the leaves, tubers are also infected by fallen sporangia. As a result the whole plant is killed. The disease can be controlled by destroying all infected plants before lifting the tubers.

7.3General characteristics of fungiOften examined

Fungi (singular: fungus) are a diverse group of eukaryotic microorganisms. They are not differentiated into roots, stems and leaves. They play critical roles in ecosystems and obtain nutrients through external digestion, secreting enzymes to break down organic matter. The group includes familiar organisms such as mushrooms, as well as microscopic molds and yeasts. Fungi are essential decomposers, form symbiotic relationships with plants, and can cause diseases in humans and crops.

Mycology

The study of fungi.

Mycologist

A person who studies fungi.

Habitat and mode of life

Fungi occupy various environments: terrestrial ecosystems such as forests and grasslands, and aquatic environments such as lakes and rivers. Some live in association with other organisms, forming mutualistic relationships, while others are parasites, decomposers or symbiotic partners with plants.

Size

The size of fungi varies from microscopic to macroscopic, depending on the species and the stage of the life cycle. Many fungi are visible only under a microscope. Yeasts are unicellular fungi that are typically a few micrometres to about 10 micrometres across. The fruiting bodies of certain mushrooms can reach from a few millimetres to several centimetres in diameter. The largest living organism on Earth is a fungus called Armillaria ostoyae (honey mushroom), which covers an area of over 2,385 acres in Oregon, USA.

Nutrition

Fungi cannot prepare their own food because they lack chlorophyll. They are therefore heterotrophic and rely on extracellular digestion. Complex organic substances such as carbohydrates and proteins are broken down by enzymes into simpler molecules, such as sugars and amino acids, which are absorbed directly through the cell walls.

Cell wall and thallus

Fungi have rigid cell walls made of chitin, in contrast to the cellulose walls of typical plants. Chitin is a nitrogen-containing polysaccharide that is more resistant to decomposition than cellulose. Fungi can store carbohydrates, but unlike plants they store them not as starch but as glycogen, like animals.

The thallus, or body, of most fungi is a multicellular structure known as a mycelium (Greek mycelium: fungus filaments; plural mycelia). A mycelium is a network of filaments called hyphae (Greek hyphae: web). Hyphae increase the surface area of the mycelium for absorption of nutrients into the body of the fungus.

Locomotion

Fungi are non-motile, lack basal bodies and do not have flagella at any stage of their life cycle. They move towards a food source by growing towards it.

Reproduction

A fungus can reproduce both asexually and sexually.

• Budding: yeasts reproduce by forming small outgrowths, or buds.
• Fragmentation: some fungi break into fragments, and each piece can grow into a new organism.
• Mitotic spores: certain fungi produce spores by mitosis, which can develop into genetically identical individuals.
• Sexual reproduction involves the fusion of specialised sexual cells and results in genetic diversity.

Why are fungi classified as a separate kingdom?

Fungi were originally classified in the plant kingdom, but more recent studies showed that they resemble animals more. Fungi are now classified as a distinct kingdom in the five-kingdom system of classification, because of several fundamental differences that set them apart from plants, animals and other organisms.

Nuclear mitosis

Hence fungi are neither plants nor animals. They show nuclear mitosis. During nuclear mitosis the nuclear envelope does not break down; instead the mitotic spindle forms within the nucleus. The nuclear membrane constricts between the two clusters of daughter chromosomes. In some fungi the nuclear envelope dismantles late.

7.4Diversity among fungi and ZygomycotaOften examined

The kingdom Fungi is a diverse group of more than 100,000 known species, most of which are terrestrial. The ancestry of fungi, which dates back to about 570 million years ago, has not been determined. They are thought to have evolved from red algae, as both lack flagella at any stage of their life cycles.

Classification of fungi

Fungi are classified into four main groups, based mainly on their methods of reproduction and the types of their sexual reproductive structures. The groups also differ in the types of hyphae and some other structures: Zygomycota, Ascomycota, Basidiomycota and Deuteromycota.

Zygomycota (conjugating fungi)

Zygomycota, also known as conjugating fungi, are typically fast-growing fungi found in various habitats, including soil and decaying organic matter. Commonly they are saprotrophs on bakery goods, vegetables and fruits. They are known for their important role as decomposers, breaking down organic material in ecosystems. Some members can be pathogenic to plants or animals. They have non-septate hyphae forming a well-developed and branching mycelium.

Asexual reproduction takes place by sporangia containing conidia or spores, for example in Rhizopus nigricans (black bread mold).

Sexual reproduction takes place by conjugation (Figure 7.15). It occurs only between a plus (+) and a minus (−) strain.

Zygospore

A diploid zygote with a thick, resistant wall, formed by conjugation in Zygomycota.

Gametangia

Specialised gamete-producing structures formed when hyphal tips of opposite strains fuse.

Conidia

Spores formed asexually (in sporangia in Zygomycota, as in Rhizopus).

Ascomycota (sac fungi)Often examined

Ascomycota, commonly called sac fungi, is one of the largest and most diverse phyla of the fungal kingdom. They are found in many habitats, from soil and wood to symbiotic relationships with plants and lichens. Many economically important fungi belong to this group, including morel and truffle mushrooms, brewers' and bakers' yeast, and several plant pathogens.

They are named after their characteristic reproductive structures, the asci (singular: ascus), which are sac-like cells containing sexually produced spores. Their hyphae usually have septa, but the cross-walls are perforated so that cytoplasm can move from one compartment to the other. Ascomycetes reproduce both asexually and sexually.

Asexual reproduction

• Production of spores called conidia (singular conidium) or conidiospores (Greek konis: dust, spora: seed). Conidia vary in shape and size and may be multicellular. There are no sporangia in Ascomycetes.
• The conidia develop directly on the tips of modified aerial hyphae called conidiophores. When released they are blown away by wind.
• The colour of conidia (brown, blue, pink or other tints) gives many of these molds their characteristic colour.
• In unicellular yeasts, asexual reproduction takes place by budding: a small projection (bud) grows and eventually separates from the parent cell, and each bud can grow into a new yeast cell. Yeast also reproduces asexually by fission.

Sexual reproduction

Dikaryotic

A state in certain fungi where a cell or hypha (a filamentous structure) contains two distinct nuclei within the same cell. The two nuclei originate from different parent cells and may have different genetic material.

Ascus

A sac-like cell in which the sexually produced ascospores are formed (usually eight).

Ascocarp

The fruiting body of Ascomycota, in which asci develop.

Basidiomycota (club fungi)Often examined

Basidiomycota, commonly known as club fungi, is a diverse and ecologically important phylum of the kingdom Fungi. It includes some of the most recognisable and economically significant fungi, such as mushrooms, rust, smut, puffballs, toadstools and shelf fungi. They are found in various habitats, often forming mycorrhizal relationships with plants or decomposing organic matter.

Basidiomycota are distinguished by filamentous hyphae. Most species reproduce sexually with basidia, specialised spore-forming structures, and the phylum is named after them. Each basidium is a club-shaped organ: a hyphal cell that typically generates groups of four spores on its tip, called basidiospores. An individual fungus produces millions of basidiospores, and each basidiospore can give rise to a new primary mycelium.

The hyphae of a primary mycelium are composed of monokaryotic (n) cells. The mycelium of a basidiomycete such as Agaricus (mushroom) consists of a mass of white, branched, thread-like hyphae that occur mostly below ground. The hyphae are divided into cells by septa, and the septa are perforated and allow cytoplasmic streaming between cells.

Life cycle of a mushroom

Although club fungi occasionally produce conidiospores asexually, they usually reproduce sexually.

Deuteromycota (imperfect fungi)

These fungi are called imperfect fungi because the sexual stage is absent from their life cycle. They reproduce asexually by forming conidiospores (conidia). The morphology and biochemistry of imperfect fungi trace their ancestry to sac fungi, which have lost the ability to reproduce sexually.

They lead a saprophytic or parasitic life on plants and have well-known economic importance. Penicillium, Aspergillus, Alternaria and Fusarium are a few examples of imperfect fungi.

Summary of the four phyla of fungi

7.5Importance of fungi: yeast and antibioticsOften examined

Fungi are important players in economic gains as well as losses. They decompose organic matter, recycling nutrients in ecosystems. They form symbiotic relationships with plants, aiding nutrient uptake. Fungi are sources of antibiotics, enzymes and food (mushrooms, yeast). They also have vital roles in research, biotechnology and as indicators of environmental health. Fungi cause diseases in humans, other animals and plants, and they cause huge agricultural damage every year.

Importance of yeast

Yeast is renowned for its pivotal role in baking and brewing, because of its remarkable ability to produce ethyl alcohol and carbon dioxide from sugars such as glucose by fermentation. It leavens dough and ferments sugars to create bread, beer and wine. It also has great implications in genetic research, serving as a model organism for scientific exploration. Its simple yet elegant biology, genetic tractability and resemblance to human genes have unlocked insights into fundamental biological processes.

Antibiotics from fungi

Fungi act like nature's medicine cabinet, giving us antibiotics and valuable compounds. Table 7.6 lists the antibiotics obtained from fungi, as printed in the book.

Mutualism: lichens and mycorrhizaeOften examined

Mutualism is the association in which both partners benefit. The two key mutualistic symbiotic associations formed by fungi are lichens and mycorrhizae.

Lichens

Lichens are an association between a fungus (mostly Ascomycetes and imperfect fungi, and a few Basidiomycetes) and a cyanobacterium or green alga. The top layer, composed of resilient fungal hyphae, is thin. In the middle layer the fungal hyphae intertwine with the photosynthetic cells, while the bottom layer consists of loosely packed fungal hyphae that facilitate nutrient transfer within the fungus.

Traditionally, lichens were thought to have a mutualistic relationship, with the fungus gaining nutrients from the algal cells and the algae receiving protection from drying out. However, recent research suggests that lichen associations may involve a controlled form of parasitism by the fungus on the algal cells.

Mycorrhizae

Mycorrhizae are mutually beneficial partnerships between soil fungi and the roots of most plants. The association occurs in 95% of all families of higher plants. Fungal hyphae play an important role by increasing soil contact and surface area, aiding the direct uptake of essential nutrients such as phosphorus, zinc and copper from the soil into the roots. Plants hosting mycorrhizae tend to grow more successfully than those without these partnerships. In return the plants give the fungi carbohydrates made by photosynthesis.

Mycorrhizae come in two primary types.

• Endomycorrhizae: these fungi penetrate plant roots, specifically the outer (cortex) cells, forming coils, swellings and tiny branches, while also extending into the surrounding soil.
• Ectomycorrhizae: these fungi create a protective layer (sheath) outside the root, growing between cell walls. They are typically associated with trees such as pines and firs.

Edible fungi

In the Orient, Aspergillus tamarii and other imperfect fungi are used to produce soy sauce by fermenting soybeans. Among the basidiomycetes there are approximately 200 varieties of edible mushrooms, primarily Agaricus, alongside about 70 potentially poisonous ones, often called toadstools. Some edible mushrooms are cultivated for commercial purposes. Notably, Morchella esculenta (a morel, resembling mushrooms) and truffles, known for their subterranean fruiting bodies, belong to the Ascomycetes.

Ecological impact of fungiOften examined

Fungi are ecological powerhouses, influencing nutrient cycling, plant health, soil formation and even the balance of predator-prey interactions. Their role in ecosystems is intricate and multifaceted, highlighting their significance in maintaining the health and sustainability of the natural world.

Pathogenic role of fungiOften examined

Fungi are causative agents of many plant, animal and human diseases. A few are discussed below.

Role of fungi in plant diseases

Fungi can cause serious diseases in plants, including epidemic diseases that can destroy complete crops. These tiny organisms threaten all crops and trees. They create problems such as leaf spots, wilting and rotting.

Role of fungi in animal diseases

Fungal diseases in animals, including humans, are diverse and range from mild skin infections to severe systemic illnesses.

Superficial infection

A fungal infection in which only the skin, hair or nails are infected.

Systemic infection

A fungal infection of internal tissues and organs that may spread through the body.

Mycotoxin

A fungal toxin, for example aflatoxin from Aspergillus flavus.

Activity 7.1STEAM activity 7.1: Rhizopus on stale bread

Aim: to observe and describe the characteristics of Rhizopus growing on stale bread.

Materials: stale bread, plastic bags, magnifying glasses or microscopes, small containers, a water spray bottle, and a drawing book or notebook for recording.

Key terms

Protist

A eukaryotic organism that is not a plant, animal or fungus; mostly aquatic and single-celled or simple multicellular.

Polyphyletic

A grouping of organisms that do not share a common evolutionary ancestor; protists and protozoa are polyphyletic.

Coenocytic

Having many nuclei in one continuous cell with no cross-walls, as in coenocytic hyphae and some filamentous algae.

Protozoa

Single-celled, animal-like protists that ingest food and move by pseudopodia, cilia or flagella.

Contractile vacuole

A vacuole of freshwater protozoa that pumps excess water out of the cell to keep the internal balance.

Pseudopodia

Cell protrusions used by amoebas for movement and feeding.

Zooflagellates

Protozoa that move using flagella, for example Giardia.

Choanoflagellate

A sessile marine or freshwater flagellate on a stalk, whose flagellum is surrounded by a collar like that of sponge collar cells.

Ciliates

Protozoa covered with cilia, for example Paramecium, Stentor and Vorticella.

Foraminifera

Marine protozoa with protective shells composed of calcium.

Actinopods

Marine protozoa whose shells are made of silica.

Apicomplexans

A large group of parasitic protozoa with complex life cycles, such as Plasmodium.

Algae

Plant-like protists with photosynthetic pigments but without roots, stems, leaves or vascular tissue.

Thallus

The branched or leaf-like body of a multicellular alga, or the body of a fungus.

Dinoflagellates

Algae with cellulose plates impregnated with silica and usually two flagella; some cause red tides or bioluminescence.

Diatoms

The most numerous unicellular algae in the oceans, with a two-part cell wall like a box and lid.

Frustules

The intricate silica shells of diatoms.

Kelps

Massive brown algae that can reach 75 m in length.

Holdfast

The base by which a red alga is anchored to rocks or other surfaces.

Plasmodium (slime mold)

A diploid, multinucleated cytoplasmic mass wrapped in a slime sheath.

Sporangium

A reproductive structure that produces spores by meiosis (slime molds) or contains spores (oomycetes, Zygomycota).

Oomycota

Water molds, white rusts and downy mildews: fungus-like protists with cellulose cell walls and coenocytic hyphae.

Zoospores

Swimming spores with a single whip-like flagellum, produced asexually in the sporangia of oomycetes.

Oogonium

The female gametangium of oomycetes, containing one to eight eggs.

Antheridium

The male gametangium of oomycetes, containing numerous male nuclei.

Oospore

The thick-walled zygote of oomycetes, a survival structure that gives the phylum its name.

Saprotroph

An organism that feeds on non-living, rotten organic matter (detritus); also called a saprophyte or saprobe.

Haustoria

Short, specialised branches of Phytophthora that penetrate leaves to obtain nourishment.

Fungi

Eukaryotic, heterotrophic, non-motile organisms with chitin cell walls that digest food externally and reproduce by spores.

Mycology

The study of fungi; a mycologist is a person who studies fungi.

Hyphae

The filaments of a fungus, which increase the surface area for absorption; they may be septate or aseptate.

Mycelium

A network of hyphae that forms the thallus (body) of most fungi.

Chitin

A nitrogen-containing polysaccharide that forms fungal cell walls and resists decomposition better than cellulose.

Glycogen

The form in which fungi store carbohydrates, as in animals (plants store starch).

Nuclear mitosis

Mitosis in which the nuclear envelope stays intact and the spindle forms inside the nucleus, as in fungi.

Budding

Asexual reproduction in which a small outgrowth (bud) separates from the parent cell, as in yeast.

Fragmentation

Asexual reproduction in which a fungus breaks into pieces that each grow into a new organism.

Zygomycota

Conjugating fungi with non-septate hyphae and a zygospore, such as Rhizopus.

Conjugation

Sexual reproduction between plus (+) and minus (−) strains in which hyphal tips fuse to form gametangia and a zygospore.

Zygospore

A diploid zygote with a thick, resistant wall formed in Zygomycota.

Gametangia

Specialised gamete-producing structures formed by fusion of hyphal tips.

Ascomycota

Sac fungi that form asci containing ascospores in an ascocarp, for example yeast, morels and truffles.

Ascus

A sac-like cell in which sexually produced ascospores form, usually eight per ascus.

Ascocarp

The fruiting body of Ascomycota where asci develop.

Conidia

Asexual spores formed on the tips of conidiophores (modified aerial hyphae) in Ascomycota and Deuteromycota.

Dikaryotic

Having two distinct nuclei (n + n) from different parents in the same cell or hypha.

Basidiomycota

Club fungi that form basidia bearing basidiospores, such as mushrooms, rusts and smuts.

Basidium

A club-shaped hyphal cell that bears four basidiospores on its tip.

Basidiocarp

The fruiting body (mushroom) of Basidiomycota, consisting of a stalk and cap with gills.

Deuteromycota

Imperfect fungi that have no sexual stage and reproduce by conidia, such as Penicillium and Aspergillus.

Parasexuality

A genetic recombination mechanism in imperfect fungi by exchange of chromosome portions between two nuclei in the same hypha.

Mutualism

An association in which both partners benefit, as in lichens and mycorrhizae.

Lichen

A mutualistic association between a fungus and a cyanobacterium or green alga.

Mycorrhizae

Mutually beneficial partnerships between soil fungi and plant roots that increase the uptake of phosphorus, zinc and copper.

Endomycorrhizae

Mycorrhizal fungi that penetrate the outer cells of the root and form coils, swellings and tiny branches.

Ectomycorrhizae

Mycorrhizal fungi that form a protective sheath outside the root and grow between cell walls, typical of pines and firs.

Toadstools

About 70 potentially poisonous basidiomycete mushrooms.

Plasmids

Small DNA molecules in yeast that can be used as gene vectors.

FBISE 2025 and 2026 questions

Questions from the FBISE HSSC-I 2026 (1st Annual) and FBISE HSSC-I 2025 (1st Annual) papers that belong to this unit, answered the way an examiner expects.

Exam focus

1. Mycorrhiza: define it and differentiate endomycorrhiza from ectomycorrhiza (position, growth, plants). (short)
   Asked as 2025 Set B Q.2 (vi), as MCQ 9 in 2025 Set D and 2026 Set B, and as book short question 17.
   Go to answer
2. Diseases caused by fungi in humans: name, cause and one symptom (ringworm, athlete's foot, candidiasis, histoplasmosis, ergotism). (short)
   Asked in 2026 Set B Q.2 (xi) OR and 2025 Set D Q.2 (xii); the book also asks about histoplasmosis (short question 20).
   Go to answer
3. Diseases caused by fungi in plants (powdery mildew, rusts and smuts, ergot of rye, brown rot). (short)
   Asked in 2026 Set D Q.2 (xi) OR; the table of plant diseases is a direct source.
   Go to answer
4. Lichens: partners, layers and what each partner gives. (mcq)
   2026 Set D MCQ 9 asks what the fungus provides; Figure 7.19 is a likely draw and label.
   Go to answer
5. Saprotrophic, parasitic and mutualistic nutrition of fungi, and external digestion. (short)
   2026 Set D MCQ 10 (saprophytes) and Q.2 (v) OR (saprotrophic against parasitic); book long question 7.
   Go to answer
6. Edible and poisonous fungi (Agaricus, Morchella, truffles, Amanita). (mcq)
   2025 Set B MCQ 10 asked which fungus is poisonous.
   Go to answer
7. Compare Zygomycota, Ascomycota and Basidiomycota: spores, fruiting body and life cycle. (long)
   No paper question from the four sets in this unit, but long questions 8 and 10 in the book and the SLOs cover the life cycles.
   Go to answer
8. Features of protists and the major groups (protozoa, algae, slime molds, water molds). (long)
   No paper question from the four sets; book long questions 1 to 5 and the SLOs cover them.
   Go to answer