Food: It is available at particular points, e.g. leaves in plants, alimentary canal in animals. Food has to be transported to every living cell of the body for extraction of energy and materials. Metabolic Gases: Oxygen and carbon dioxide are two metabolic gases. Oxygen is required by every living cell for cellular respiration. It has to be transported from outside environment first to the respiratory surfaces and then to individual cells in animals or directly to cells in plants. Carbon dioxide is formed as a by-product. It is passed out for elimination. Waste Products: Toxic waste products are produced during metabolism. They have to be excreted. For this they are first taken to kidneys for separation, translocated to urinary bladder for storage and from urinary bladder to the region of elimination. Water: Plants absorb water from soil with the help of their roots. It is transported to all parts. Hormones: They are formed in particular regions from where they are transported to the areas of their functioning.
Respiratory centre is in Medulla Oblongeta. Mechanism of breathing involves Two Phases. (A) Inspiration (B) Expiration Inspiration: Intercostal and phrenic muscles of diaphragm contract to increase thoracic cavity, therefore outside rushes inside. Expiration: Intercostal & phrenic relex muscles. Due to decrease of thoracic cavity air pressure within lungs increase, the greater pressure within lungs force ful air from lungs to outside of body. Gaseous Exchange: Gaseous exchange occur in Alveoli following pressure gradient O2 from high pressure in alveoli diffuse into blood & CO2 from blood in alveoli. Gaseous Transport: O2 is carried by haemoglobin (in RBC). 100 ml of blood can carry ~20 ml of O2 max, CO2 is transported in form of bicarbonates in plasma.
The mammalian respiratory system consists of nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles and alveoli. Nostril: It is also called external nares. Nasal Chamber: Nasal septum divides nasal cavity into two nasal chamber by the nasal septum. Internal nares: There are posterior opening of nasal chambers that leads into pharynx. Pharynx: The pharynx provides passage to both air and food. Laryngopharynx: It is the lower part of pharynx and has a slit like aperature called glottis, which can be closed by a leaf like bilobed cartilage epiglottis, during swallowing of food bolus. Larynx: It is also called voice box or adam’s apple or pomas adami. Vocal cord: In larynx, 2 pairs of vocal cord is found outer pair is false vocal cord whereas, inner pair is true vocal cord when air is forced through the larynx it cause vibration of true vocal cords and sound is produced. Trachea (Wind pipe): It is long, tubular structure which runs downward through the neck in front of oesophagus. It is supported by cartilage to prevent collapse. Primary bronchi: These are one pair of small thin walled tubular structure formed by the division of trachea. It further divides and end at alveoli. Lungs: lungs are present in thoracic cavity on either side of heart. covered by pleural membrane.
By young roots: Air occurs in soil interspaces. Root hairs as well as epiblema cells of the young roots are in contact with them. They are also permeable to metabolic gases. Oxygen of the soil air diffuses through root hair-epiblema cells and reaches all internal cells of the young root. Carbon dioxide produced by root cells diffuses in the opposite direction. By Leaves: Leaves and Young Stems. Leaves and young stems are ideally suited to quick exchange of gases. The organs have a covering of nearly impermeable epidermis for reducing loss of water. The epidermis of leaves bears a number of aerating pores called stomata (singular stoma or stomata, Gk. stoma-mouth). Each aerating or stomatal pore is bordered a pair of guard cells. In most of the plants, the guard cells are kidney or bean shaped with inner walls being thicker and less elastic than the outer walls. When the stomata are open, gases diffuse into and out of the leaf as per their concentration gradient. A gas which has come from outside first reaches substomatal chambers. From here, it diffuses to all the intercellular air spaces present in between the mesophyll cells. If the stomata are open during night, oxygen from outside will diffuse into the leaves and young stems while carbon dioxide will diffuse out. It is due to respiratory gas exchange.
Photosynthesis: Photosynthesis is the primary mode of food production in green plant. ” The process by which green plants synthesize food from simple substances carbon dioxide and water in the presence of sunlight is called Photosynthesis” The process of photosynthesis can be represented in the form of chemical reaction, as given below : 6CO2 + 12H2O → C6H12O6 + 6H2O + 6O2 Carbon Water Glucose Water Oxygen dioxide
Photosynthesis
Conditions Necessary for Photosynthesis The general conditions necessary for photosynthesis are: • The presence of a green pigment called chlorophyll. • The presence of light. • The availability of carbon dioxide. • The availability of water.
Photosynthetic Pigment: The light energy must be absorbed by a suitable pigment i.e. chlorophyll (green pigment). Chlorophyll is green colour pigment.
Mechanism of Photosynthesis: Photosynthesis is divided in 2 main steps (A) light reaction (B) dark reaction
Light reaction: It is also called Hill Reaction. It occurs in grana of thylakoids. It is named as light reaction as it occurs only in presence of light.
Inside a chloroplast
Water: The root system of plants enables them to obtain water from the soil. The root system consists of a main or primary root, rootlets or secondary roots, and root hair. Root hair increase the surface area of roots, and are found in great numbers near the tips of roots. Water and soluble nutrients travel through the root system and reach the leaves. Water and soluble nutrients are transported from roots to other parts of the plant through structures called xylem. The starch formed as a result of photosynthesis is transported to the various parts of the plant by structures called phloem.
Root system
Major Step: Absorption of light by chlorophyll. Photolysis of water. Reduction of CO2 to Carbohydrates. In this process ADP changes to ATP & inorganic phosphate. Release of oxygen into atmosphere.
Opening and Closing Stomata: The opening and closing of stomata depend upon the turgid or flaccid state of the guard cells. When guard cells are in turgid state the stomatal aperture opens and when guard cells are in flaccid state the stomatal aperture closes. The inner wall of guard cells (towards pore) is thick and outer wall (towards other epidermal cells) is thin. When the turgor pressure of the guard cells is increased the outer thinner wall of the guard cell is pushed out (towards the periphery) due to which a tension is created on the inner thicker wall thus pulling the inner thicker wall towards the periphery thus leading to the opening of stomatal aperture. On the contrary when the guard cells are in a flaccid state the outer thinner wall of guard cells returns to original position (moves towards pore) due to which tension on the inner wall is released which also returns to its original position and stomatal aperture gets closed again.
Dark Reaction: This reaction is not dependent on light. It is also known as calvin – Benson Cycle or C3 cycle as first stable product is phosphogliceric acid (PGA) a 3 carbon compound.
C4 Cycle or Hatch & Slakcycle: 4-C compound i.e. oxaloacetic acid (OAA). This cycle is found in many other tropical & subtropical monocots eg : Maize, Sorghum , Wheat, Oat, Pearl, millet etc. In dicots also many such plants are known eg : Amaranthus, Chenopodium, Atriplex, Euphorbia etc. In some families of dicots Compositae, Portulaceae, Nyctaginaceae.
Crassulacean Acid Metabolism (CAM): Certain plants, especially succulents which grow under extremely xeric (dry) condition, fix atmospheric CO2 in dark. Since the process was first observed in the plants belonging to family crassulaceae (eg. Bryophyllum, kalanchoe etc.) It was termed crassulacean acid metabolism (CAM). The most characteristic feature of these plants is that their stomata remain open at night (in dark) but closed during the day (in light). Thus, CAM is a kind of adaptation in succulents to carry out photosynthesis without much loss of water.
Activity 1
Aim: To find out if light is necessary for photosynthesis Materials needed: Green plant, black paper, scissors, and clip Method:
Cover a part of a leaf using a strip of black paper.
Place the plant in a dark corner for three days.
Pluck a leaf from the plant and test it for starch to confirm whether it is fully starch-free.
Now place the plant in sunlight for at least six hours.
Pluck the leaf covered with the strip of black paper, remove the strip, and test the leaf for starch.
Observation: The covered portion of the leaf shows no change when iodine solution is added. Conclusion: There was no starch formation in the covered part, so this part did not turn blue-black. This shows that light is necessary for photosynthesis.
Activity 2
Aim: To demonstrate that carbon dioxide is needed for photosynthesis
Materials needed: A potted plant, potassium hydroxide solution, a conical flask with a split cork, iodine solution, and a dropper Method:
Keep the potted plant inside a dark room for a few hours. Water it.
Pour potassium hydroxide solution into a conical flask. The solution absorbs carbon dioxide from the air.
Place one of the leaves (without breaking it from the plant) inside the flask and cork it.
Now, keep the entire arrangement in sunlight.
After a few hours, test the leaf in the flask and another leaf for starch, using iodine solution.
Observation: When iodine solution is added, the leaf clasped inside the conical flask shows no change, whereas the other leaf turns blue-black. Conclusion: The leaf inside the conical flask did not carry out photosynthesis because there was no carbon dioxide available to it.
