حصريا : شرح درس The aquatic environment - علوم لمدارس اللغات للصف الاول الاعدادى

تاريخ التسجيل : 30/03/2010

Introduction

Water covers about 71% of our planet’s surface most of which is salt water (seas and oceans) and some fresh water (rivers), the fresh and salt water is different from the point of: water clarity and turbidity, dissolved oxygen content, dissolved salts and speed of water currents.

Objectives:

Recognize the adaptation of some plants to live in fresh water environment.
Recognize the adaptation of some animals to live in fresh water environment.
Recognize the adaptation of some plants to live in saline water environment.
Recognize the adaptation of some animals to live in saline water environment.

Fresh water plants and their adaptation to fresh water conditions

The Elodea plant:

This plant is found in the still water in irrigation and drainage canals. Structure:

The roots: are free from hairs since it absorbs water and dissolved salts by all plant parts.
The stem: is green, elastic and flexible to overcome the effects of water currents.
The leaves: are small, thin, ribbon like and green so they will not be cut by water currents.
Note that: by examining a section in the stem of elodea plant, you will notice the presence of large air vacuoles which store the produced oxygen gas of photosynthesis process to be used in respiration when it is needed and to keep the plant floating in the water.

Lotus:

Is found in the water of irrigation and drainage canals and by the Nile river shores.
Some parts of the plant are immersed in the water while other parts are floating above the water surface.
There are two kinds of this plant: white lotus (with white flowers) and blue lotus (with blue flowers).
The lotus flower was used by Ancient Egyptians as the symbol of the country.

Structure:

The roots: weak and absorb water and dissolved minerals.
The stem: is a creeping stem.
The leaves:
Characterized by Long, thin and flexible petioles to overcome water currents, the petioles extend to the water surface and end by leave blades.
The blade is large and flattened and floats on the water surface.
The upper surface of the Lotus leaves are full of pores which permit the entrance of air and its contents of carbon dioxide which is necessary for photosynthesis which is carried by the green parts of the plant.

The adaptation of aquatic plants to the fresh waters conditions:

To overcome the shortage of light:

The plants may live floating on the water surface or immersed near the water surface to receive enough light for their photosynthesis process.
The green plastids are distributed in the surface cells in each of the leaf and the stem in the immersed plants to carry on the photosynthesis.

To overcome the shortage of oxygen:

Some plants contain wide air vacuole to store oxygen produced from the photosynthesis process to be used when it is needed.
The air vacuole help in floating the plants.

To overcome the effect of water currents:

The weak roots of the aquatic plants are not used to fix the plants therefore, it can move easily with water currents from one place to another.
The stems of the immersed plants and the petioles of floating plants leaves are free of supporting tissues so it will not break
The leaves of the immersed plants are thin and ribbon like.

Fresh water animals and their adaptation to fresh water conditions

Bolti Fish:

Lives in fresh water as well as in salt water and is abundant in the River Nile and its branches.
The body is flat at the two sides and silvery blue in color.
The body is covered with scales that are fixed from the front and there are circular rings on the scales that tell the age of the fish.
The body consists of: Head, trunk and tail

The head consists of:
- The mouth: an opening at the head front.
- The nose: two small opening above the mouth opening and are used for smelling only..
- The eyes: two large openings without lids.
- The gills openings: two large openings at the head end, each is covered by gill lid.

The trunk:

Starts after the head and extends from the back edge of the gill lid till the anal opening and is covered with scales.
In the male fish, there are two openings which are the anal and the urine genital openings.
In the female, there are three openings which are the anal, the genital and the urinary openings.

The Tail:

Follows the trunk and is covered with scales, it is the main movement organ..
There are two lateral lines on the trunk and tail sides to enable the fish to feel sound waves and the changes in water pressure.

The fins: there are two kinds of fins:

Single fins: dorsal fin, anal (ventral) fin and tail (caudal) fin.
Double fins: two pelvic and two pectoral fins.
Fins Keeps the fish balanced in water and directs its movement..

Bolti fish movement:

The fish moves forward by flapping its tail fin to the left and right.
When the fish keeps the left pelvic and pectoral fins stable and moves the right fins, it turns to the left.
The fish ascend and descend by the help of the air bladder .

The air bladder:

A closed bag located below the vertebral column, this bag have thin walls filled with air.
When the air bladder is filled by air, the fish ascends.
When the fish removes some of the air from the air bladder, the fish descends in the water.

Respiration in Bolti Fish:

Fish respires by the gills.
Pulling the gill covers (operculum), we notice that each covers a chamber that contains four gills with thin walls.
Blood capillaries spread in the gills to facilitate the exchange of gases between the blood in the capillaries and the dissolved oxygen in water.

The adaptation of Bolti fish to the fresh waters conditions:

The streamline of their bodies gives them the chance to move easily.
The fins help in balancing and changing the direction.
The gills extract dissolved oxygen in water for respiration.
The body is dark from the top and bright from the bottom to hide from enemies.

Saline water environment

Most of the marine organisms live near the beach or in the surface waters. Marine plants:

There are many marine plants the most important of which are algae.
Algae are different in shape, size and structure and some can only be seen under microscopes.
Some algae are considered the longest of marine plants and are called seaweeds with a length of 190 meters in the arctic area
Marine plants are primitive plants called algae.
Algae produce food and oxygen gas through photosynthesis process.
There are many kinds of algae such as green, yellow and brown algae.

The economic importance of algae:

Algae are important because they produce food through the photosynthesis and produce oxygen for their respiration, also marine organisms depend on the oxygen produced by the algae in their respiration.
Some algae are edible by man such as the red algae while most marine organisms depend on algae for their food.
Some brown algae are used in food industries.
Some kinds of algae are used in making jelly materials called Agar which is used in microbial culture in medical and biological fields.
Some kinds of seaweeds are used as fertilizers for agriculture lands near the sea shores.

Marine animals:

In the sea water, there are different kinds of vertebrate and invertebrate organisms. The vertebrate:

Some have bone skeletons like Bolti, Bouri, Arous, Salmon, Tuna and Herrings
Some have cartilage skeletons like the shark and sea fish.

The invertebrate:

Like Shrimp, Sponge, Om-Kholool, El-Gandofly and Morgan.