TOPIC 1. CLASSIFICATION KINGDOM FUNGI

                       Movement of water through leaves

Note: Another process known as guttationalso occurs in plants. It is the process by which plants lose water as droplets through special glands found where veins are in contact with the leaf margin. Guttation is different from transpiration in that transpiration is the loss of water vapor mainly through the plant's stomata. Guttation occurs mostly at night or in plants growing in wet areas

Types of transpiration

There are three types of transpiration:

1. Stomatal   transpiration   occurs   through the stomata on the leaves. It accounts for approximately 90% of the water lost by plants.
2. Cuticular   transpiration   happens   through the cuticle of leaves. The cuticle is a waxy layer that covers the surface of leaves. A thick cuticle prevents excessive loss of water.
3. Lenticular transpiration takes place through the lenticels. Lenticels are pores found on the bark of stems or roots in woody plant

Factors affecting the rate of transpiration

The rate of transpiration is affected by plant features as well as environmental factors.

Plant features

Plant features include the following:

(a)    The size of leaves; a large leaf has more stomata than a small leaf. Therefore, plants with large leaves lose more water than those with smaller leaves,

(b)   An extensive root system:Plants that have extensive roots absorb more water and can therefore lose more water than those with few roots.

(c)    Leaf cuticle: A thick cuticle resists water loss by transpiration while a thin cuticle makes water loss by transpiration easier.

(d)   Number of stomata: The more stomata a leaf have, the faster the rate of transpiration and vice versa.

(e)   Position of stomata:Stomata on the upper surface of the leaf lose water more easily than those on the lower surface. If a plant has leaves with more stomata on the upper surface, the rate of transpiration is faster than in        a plant that has Leaves with more stomata on the lower leaf surface.

(f)    Size of substomatal air spaces: Larger air spaces allow for a faster rate of transpiration because the leaves can hold more water vapor. Smaller substomatal air spaces slow down the rate of transpiration.

(g)   Sunken stomata: Sunken stomata occur in pits. They are not exposed to moving air so they slow down transpiration rate.

(h)   "Epidermal hairs: Epidermal hairs trap water on the surface of the leaves, thus preventing water

Environmental factors

(a)    Temperature: Transpiration rates go up as the temperature goes up. Higher temperatures cause the stomata to open and release water into [the atmosphere. Lower temperatures cause the stomata to close.

(b)   Relativehumidity:As the relative humidity of the surrounding air rises, the transpiration rate falls. It is easier for water to evaporate into dry air than into air saturated with moisture.

(c)   Wind and air movement: Increased movement of the air around a plant results in a higher transpiration rate. As water transpires from a leaf, the water saturates the air surrounding the leaf. If there is no wind, the air              does not move, thus 11raising the humidity of the air around the leaf. Wind moves the air causing the more saturated air close to the leaf to be replaced by drier air.

(d)   Availability of soil moisture:When moisture is lacking in the soil, plants begin to senesce (age prematurely) resulting in leaf loss and reduced transpiration. Also, less water is absorbed by the roots when the soil is dry.

(e)   Light: Increased sunlight increases the rate of photosynthesis in the guard cells, causing them to become turgid and open the stomata. Higher light intensity also increases the plant's internal temperature and hence                    increases the rate of transpiration.

(f)    Atmospheric pressure: When atmospheric pressure is low, for example at high altitudes, plants lose water more easily. The rate of transpiration is reduced in areas with high atmospheric pressure.

Significance of transpiration

1. It helps to maintain transpirational pull which is important for maintaining a constant stream of water between the roots and the leaves.
2. Transpiration enables the loss of excess water from the plant,
3. It helps to cool the plant and enables absorption and distribution of water and mineral salts.

Summary:

1. The vascular system in plants is made up of xylem and phloem tissues.
2. Xylem transports water and" mineral salts from the roots to all parts of the plant.
3. Phloem transports manufactured food from the site of photosynthesis to all parts of the plant.
4. The distribution of vascular bundles is different in roots and stems and in dicotyledonous and monocotyledonous plants.
5. Root hairs are extensions of the epidermal cells of the root. They absorb water and mineral salts from the soil.
6. Water is absorbed from the soil by osmosis.
7. Mineral salts are absorbed from the soil by active transport.
8. Water and dissolved minerals move up thexylem by transpiration pull, capillarity and root pressure.
9. Transpiration is the process by which plants lose excess water through their leaves. Transpiration is important because it:

• Helps   to maintain the transpirational stream
• Enables the loss of excess water
• Enables absorption and distribution of
• Water and mineral salts in a plant
• Helps to cool the plant.

1. Transpiration is affected by the features ofthe plant and environmental factors. The features of the plant include: leaf size, size of root system, size of leaf cuticle, size of air spaces, number and position of stomata and whether the stomata are sunken or not, and the presence of epidermal hairs.
2. Environmental factors include the amounts of moisture in air, temperature, and air movement, availability of soil moisture, light and atmospheric pressure.

 GESIOUS EXCHANGE

GASEOUS EXCHANGE AND RESPIRATION

         Gaseous exchange

Gaseous exchange is the movement of oxygen and carbon dioxide across a respiratory surface. Unicellular organisms carry out gaseous exchange by diffusion across the cell membrane. Large organisms cannot carry out diffusion efficiently so they have developed specialized organs for gaseous exchange. These are called respiratory surfaces.

Table below shows examples of respiratory surfaces in various organisms. Respiratory surfaces in various organisms       

Organism	Respiratory surface
Amoeba	Cell membrane
Insects	Tracheal system
Spider	Book lung
Fish	Gills
Plants	Leaves, stems, roots
Amphibians	Skin, gills and lungs
mammals	Lungs
Birds	Lungs
Reptiles	Lungs

Characteristics of respiratory surfaces

1.  They are thin to reduce the diffusion distance.

2. They are moist to dissolve gases so that they diffuse in solution form.

3. They are highly branched, folded or flattened in order to increase the surface area for gaseous exchange,

4. They are close to an efficient transport and exchange system so that gases can be taken to and from the cells easily.

5. They are well ventilated so that gases can pass through them easily

                             GASEOUS EXCHANGE IN MAMMALS

The components of the gaseous exchange system in mammals include the nostril, trachea, lungs, intercostals muscles, diaphragm and ribs.

 

The adaptations and functions of parts of the mammalian respiratory system

Part	Adaptive features	Functions
Nose and nasal cavity	Mucus lining and hairs (cilia)	Trap dust and microorganisms
Glottis	Presence of epiglottis	Closes the trachea during swallowing to prevent food from entering the respiratory system
Trachea, bronchus and bronchioles	Blood vessels near the surface	Warm the air
	Have rings of cartilage tissue along their length	Prevent collapse of the respiratory tract
	Mucus lining and cilia	Trap and filter dust and microorganisms
Lungs	Spongy with air spaces (alveoli)	Main organ of mammalian gaseous exchange Airspaces hold inhaled air
Alveoli (singular: alveolus)	Numerous in number	Provide large surface area for gaseous exchange
	Thin membranes	Reduce distance for diffusion of gases
	Moist surface	Enables gases to dissolve into solutions before diffusing
	Has dense network of capillaries	Transport oxygen from the alveoli to the tissues and carbon dioxide from the tissues to the alveoli
	Constantly contain air	Maintain shape to avoid collapsing
Pleural membrane	Contain pleural fluid	Lubricates the membranes so that the lungs can slide smoothly over the thoracic cavity during breathing
Ribs	Are made of hard bone tissue	Protect the lungs from injury
Intercostal muscles	Move antagonistically: when one muscle contracts the other relaxes and vice versa	Allow expansion and contraction of the thoracic cavity
Diaphragm,	Muscular sheet of tissue	Separates the thorax from the abdomen. Allows for gaseous exchange by becoming dome-shaped or relaxing

The mechanism of gaseous exchange in mammals

Gaseous exchange in mammals happens as a result If inhalation (or inspiration) and exhalation (or expiration). Inhalation is breathing in air into the lungs. Exhalation is breathing out air from the lungs

During inhalation the muscles of the diaphragm Contract, pulling the diaphragm downwards; As this happens, the external intercostal muscles contract and pull the ribcage upwards and outwards. The result of these movements is an increase in the volume and a decrease in the air pressure of the thorax. This makes air rush into the lungs through the nostrils, trachea and bronchioles.

During exhalation, the muscles of the diaphragm relax and the diaphragm resumes its dome shape. The external intercostal muscles relax, pulling the ribcage inwards and downwards. As a result, the volume of the thorax decreases and the pressure inside it increases. This forces air out through the bronchioles, trachea and nostrils

	Breathing   in (inhalation)		Breathing out (exhalation)
	External intercostal muscles contract		The external intercostal muscles relax
	Internal intercostal muscles relax		The internal intercostal muscle contract
	The ribcage is rifted outward and upward		The ribcage move inward and downward
	The diaphragm contracts and flattens		The diaphragm relaxes and become dome-shaped
5	The volume of thoracic cavity increase as pressure decrease This allow air to enter the thoracic cavity	5	The volume of thoracic cavity decrease as pressure increase
6	Air enter the alveoli through the nostrils, pharynx, glottis, trachea, bronchioles and finally alveoli	6	Air leaves the alveoli through the bronchioles, trachea, glottis, pharynx and finally nostrils