(6a) Structure of FUNGAL CELLS

(examples of unicellular eukaryotes)

Fungi (eukaryotic organisms) are organisms that are not able to carry out photosynthesis; the bodies of fungi are usually organised into a multi-celled mycelium made from thread-like structures called hyphae, which contain many nuclei.

Certain fungi are single-celled and their cells have walls made of chitin; they feed by extracellular secretion of digestive enzymes onto food material and absorption of the broken down organic products; this is known as saprotrophic nutrition; they may also store carbohydrate as glycogen.

Examples include mucor, which has the typical fungal hyphal structure, and yeast, which is single-celled fungus.

Fungal cells share some similarities with plant and animal cells, but are different to both these groups.

Fungi can include yeasts (see below) and mushrooms.

In common with plant and animal cells, fungal cells have a (1) cytoplasm, 3 organelles (2) nucleus, (3) ribosomes, (4) mitochondria (mitochondrion) and a (5) cell membrane.

For details of (1) to (5) see animal cell features,

and note these details are NOT repeated here.

Some differences are:

Unlike animal cells, fungal cells have a cell wall like plant cells (with an inner cell membrane), but made of chitin rather than cellulose,

and like animal cells, they have no chloroplasts, unlike plant cells, which do have chloroplasts for photosynthesis.

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(6b) YEAST CELLS (unicellular eukaryotes)

(Yeast can be considered a unicellular fungi)

In common with plant and animal cells, yeast cells have a (1) cytoplasm, 3 organelles (2) nucleus, (3) ribosomes, (4) mitochondria (mitochondrion) and a (5) cell membrane.

For details of (1) to (5) see animal cell features,

and note these details are NOT repeated here.

Yeast is used in the production of alcoholic beverages eg beer, wine etc. and in bread making.

A yeast cell has the same organelles as a mature eukaryotic cell.

A yeast cell, a single-cell microorganism, has a nucleus, cytoplasm, mitochondria enclosed in a cell membrane which is surrounded by a cell wall.

Yeast can be regarded as a single celled fungus.

Used in fermentation e.g. brewing and bread making.

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Key points - Summary of ideas

Based on the syllabus-specifications for students taking the AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10).

Revision Notes: Structure of Yeast (Fungal Cells)

Yeasts are unicellular fungi, commonly found in diverse environments, including soil, plant surfaces, and the human body.

They are eukaryotic organisms, meaning their cells contain a nucleus and other membrane-bound organelles.

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Structure of Yeast Cells & Function of Organelles

Yeast cells contain the following structural components:

Organelle/Structure	Function
Cell Wall	Made of chitin (instead of cellulose like plants); provides rigidity and protection while allowing passage of nutrients and waste.
Cytoplasm	Jelly-like substance where biochemical reactions occur. Contains organelles like the nucleus and ribosomes.
Nucleus	Contains genetic material (DNA) stored as chromosomes. Controls growth, reproduction, and gene expression.
Ribosomes	Small structures responsible for protein synthesis. Found freely in the cytoplasm or attached to the endoplasmic reticulum.
Inner Cell Membrane (Plasma Membrane)	Regulates transport of nutrients, gases, and waste in and out of the cell via active and passive transport.
Mitochondria	Site of aerobic respiration, producing ATP (energy) for cellular functions.
Vacuole	Stores nutrients, enzymes, and waste products. Helps regulate internal cell pressure.

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Yeast as a Unicellular Organism

• Unlike most fungi, which form large structures (hyphae and mycelium), yeast exists as single cells.

• They reproduce asexually through budding, where a new cell grows from the parent cell.

• Can survive in anaerobic and aerobic conditions, allowing them to be used in fermentation processes.

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Summary of learning objectives and key words or phrases

Know the structure of yeast cells, fungi cells and fungal cells growth and the function of the organelles in these cells and be able to describe the function of the cell wall, inner cell membrane, and cytoplasm as well as the nucleus and ribosomes.

Be able to identify them in unicellular organism diagrams of yeast cells and fungal cells,

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