FUNG AND ROOT

Introduction

In unit 4, you learnt about the Prokaryotes and Eukaryotes. You learnt about bacteria as an example of the Prokaryotes. You learnt that these groups are mainly unicellular. Their cell division is mainly by binary fission, they do not have spindle. The cell walls are rigid and contain polysaccharides with amino acids; murein is main strengthening compound. In this unit you will study Fungi. Fungi belong to the group called Eukaryotes. They are mainly multicellular. Cell division in fungi is mitosis, meiosis or both. Spindle is formed in this group.

Fungi General Description

Fungi are a large group of organisms. They range from unicellular yeast to toadstool, puffballs, stinkhorns. Toadstool and puffballs are a kind of mushrooms. You must have seen some mushrooms or even eaten some. Some of them are poisonous. They are very numerous, about 80,000 species have been identified. They have some benefits to man. We have just mentioned the mushrooms that are used for food. Others are used for medicine. Yeast is used as raising agents in bread baking..
You must have seen bread with some growth on it. We usually refer to such as moulds. There are different kinds of moulds. Some grow on leather products, like shoes, handbags, rotten vegetable etc. Some grow on fruits causing damage to such fruits while others grow on plants causing the disease of plant mildews, smuts and rusts. Those who study fungi in detail are called Mycologists called and the filed itself is called Mycology.


Mucor is a typical fungus. It is made up of hyphae- branches that are like twigs, a single
one is called hypha. The hypha is hollow inside. The collection of hyphae is called mycellium. The structure of hyphae is segmented like, this segment is called septa. It divides the hyphae into compartments similar to cells, but in this case the hyphae are not divided into true cells. The hyphae contains chitin. Chitin is a nitrogen containing polysaccharide. A hypha may have cross-walls (septate) as in penicillium or lack cross- walls (aseptate) as in mucor. The cytoplasm like any Eukaryotes cell contains mitochondria, golgi apparatus, endoplasmic reticulum, ribosomes and vacuoles.

 Classification and Characteristics of Fungi

Kingdom Fungi - General Characteristics

Heterotrophic nutrition because they lack chlorophyll and are therefore non- photosynthetic. They can be parasites, saprotrophs or mutualists. Nutrition is absorptive, digestion takes place outside the body and nutrients are absorbed directly. Digestion does not take place inside the body, unlike animals. Rigid cell walls containing chitin as the fibrillar material. Chitin is a nitrogen containing
polysaccharide, very similar in structure to cellulose. Like cellulose it has high tensile strength. It therefore give shape to the hyphae and prevents osmotic busting of cells. Body is usually a mycellium, a network of fine tubular filaments called hyphae. These may be septate (have cross-walls), e.g. Penicillium, or

Uses of Fungi

1.  Yeast - different species and strains of yeast are used in the brewing industry for alcoholic fermentation. 
2. Penicillium - a blue-green mould is the source of the world famous penicillin (an antibiotic). Certain species of penicillium are used industrially in making various organic acids and in making special types of flavoured cheese. 
3. Aspergillus - is economically an important fungus. Some species are used industrially in the manufacture of alcohol from rice starch, and manufacture of certain organic acids (e.g. citric, gluconic acid) on a commercial basis. Some species are sources of certain antibiotics. 
4.  Agaricus (Mushroom) use as food by humans. 

Sum mary

Fungi are diverse in nature. There are about 80,000 species known. They could be more. Some of them are very beneficial to man like the mushrooms„ while some are destructive. If you leave your eba or bread outside for long, the spores fall on it and start to grow. The spores are found in the air, even in your refridgerator. The refridgerator does not destroy them but slow down their activity.

Root

Introduction

In Unit 7 you studied the algae you learnt that the algae belong to a large group called protoctists. They are found in water or moist areas. You learnt that they are plant - like and photosynthetic. The Chlorella was chosen as a typical example of algae, it has an evolutionary importance. In this unit, you will study the root of flowering plants. Generally the root is the part of the flowering plant that is below the soil. There are different types of roots. Some roots are modified for certain purposes

TYPES OF ROOTS

You will learn in this unit about different types of roots. You have two main kinds of roots. (You will study other types in future botany) Roots of monocotyledon are fibrous in nature and are referred to as fibrous roots. Roots of dicotyledon grow down wards and are known as tap root.

Parts Of a Root

You learnt that the root has many parts in the examination of the inner structure. Looking at the external structure, we can divide the root into:

Root- cap

You have studied the root hairs, how they push their way through the soil. In the process of pushing its way through the soil, the tip of the root needs protection because the tip is delicate. The tip of the root has a covering called root cap.

 Growing Apex of the Root

Immediately after the root cap is a region where cells divide. The cell of this region are tiny, with thin wall and contain a dense mass of protoplasm. It is also known as meristematic region - region of cell
division

Region of Elongation:

The region following the region of cell division is the region of elongation. The cells of this region undergo rapid elongation and enlargement, and are responsible for growth in length of the root.

 Region of Maturation:

Above the region of elongation is the region of maturation. This region extends upwards. The root-hairs are found in this region. In the cross- section of the root you saw in section -. You learnt that this region, is where matur ation and differentiation take place, differentiation into various kinds of primary tissue.

Region of Secondary tissues:

The region of maturation merges into the region of secondary tissues. Go back and look at the internal structure of the root again, you will see the beginning of the primary tissue and the end where it merges with the secondary tissues.

Characteristics of roots

How do we know that a structure is a root not a stem? It is a root if it;

1. Is not green in colour, descends below the soil 
2. Does not bear buds expect in sweet potatoes and some few other roots 
3.  Ends in and is protected by a cap the root-cap. 
4. Bears unicellular hairs 
5.  Develops from an inner layer (pericycle) i.e the lateral roots. They are therefore said to be endogenous (inner producing). There are branches that produce from a few outer layer and are said to be exogenous 
6.  Does not have nodes and internodes as in the stem 

 Modif ied Roots

There are many ways roots have formed or are modified for certain purposes.

1. Tap root modified for storage of food e.g in carrot, radish, yam. 
2. Branched root modified for respiration. Many plants like the mangroove growing in marshy places and salt lakes, develop special kinds of roots called respiratory roots for respiration. 
3. Adventitious roots modif ied for storage of food, e.g sweet potatoes, cassava.. 
4. Prop or stilt roots. These roots grow Vertically or obliquely downwards and penetrate into the soil, gradually they grow in stature and act as pillars to support part of the branches or even the plant itself. 
5.  Climbing roots 
6. Buttress roots 
7.  Sucking roots 
8. Respiratory roots Assimilation roots 

Roots are the structure of flowering plants that are generally below the soil the root has three regions, root caps, growing apex, region of elongation and region of maturation. Roots have various modifications: Some have been modified to store food for the plant. The yams, Cassava and carrot are typical examples of root modification.