Biology · Class 9-10 · CBSE
Life Processes: Nutrition, Photosynthesis and Digestion
Master autotrophic nutrition (photosynthesis light/dark events, stomata mechanism), heterotrophic modes (holozoic, saprophytic, parasitic), and the step-by-step human digestive system with enzymes and absorption.
1Autotrophic Nutrition and Photosynthesis
Autotrophic Nutritionis the process where green plants synthesize their own organic food from inorganic raw materials (CO₂ and H₂O) in the presence of sunlight and chlorophyll viaPhotosynthesis.
Balanced Equation of Photosynthesis
Three Sequential Events of Photosynthesis
- 1
1. Absorption of light energy by chlorophyll pigment located in thylakoid membranes.
- 2
2. Conversion of light energy to chemical energy and Photolysis of water: splitting water into hydrogen (H⁺), electrons, and oxygen gas (O₂).
- 3
3. Reduction of carbon dioxide by hydrogen to form carbohydrates (glucose).
Opening and Closing Mechanism of Stomata
| State | Guard Cell Turgor Status | Water Movement | Stomatal Pore Condition |
|---|---|---|---|
| Open Stoma | Guard cells absorb water and swell (turgid) | Endosmosis of water into guard cells | Curved outer thin wall pulls inner thick wall apart; pore opens |
| Closed Stoma | Guard cells lose water and shrink (flaccid) | Exosmosis of water out of guard cells | Elastic inner thick walls collapse straight; pore closes to conserve water |
Open Stoma
- Guard Cell Turgor Status
- Guard cells absorb water and swell (turgid)
- Water Movement
- Endosmosis of water into guard cells
- Stomatal Pore Condition
- Curved outer thin wall pulls inner thick wall apart; pore opens
Closed Stoma
- Guard Cell Turgor Status
- Guard cells lose water and shrink (flaccid)
- Water Movement
- Exosmosis of water out of guard cells
- Stomatal Pore Condition
- Elastic inner thick walls collapse straight; pore closes to conserve water
2Heterotrophic Nutrition Modes and Amoeba Feeding
Modes of Heterotrophic Nutrition
| Mode | Feeding Mechanism | Digestive Location | Organisms |
|---|---|---|---|
| Holozoic | Ingestion of solid complex organic food, followed by internal digestion and absorption | Internal alimentary tract / food vacuole | Humans, Amoeba, Cow, Lion |
| Saprophytic | Secretion of digestive enzymes outside the body to break dead organic matter into liquid, then absorbed | External breakdown outside organism body | Fungi (mushrooms, bread mould Rhizopus, yeast) |
| Parasitic | Deriving nutrients directly from living host body without killing it immediately | Host tissue fluids absorbed directly | Cuscuta (Amarbel), tapeworm, roundworm, ticks, leeches |
Holozoic
- Feeding Mechanism
- Ingestion of solid complex organic food, followed by internal digestion and absorption
- Digestive Location
- Internal alimentary tract / food vacuole
- Organisms
- Humans, Amoeba, Cow, Lion
Saprophytic
- Feeding Mechanism
- Secretion of digestive enzymes outside the body to break dead organic matter into liquid, then absorbed
- Digestive Location
- External breakdown outside organism body
- Organisms
- Fungi (mushrooms, bread mould Rhizopus, yeast)
Parasitic
- Feeding Mechanism
- Deriving nutrients directly from living host body without killing it immediately
- Digestive Location
- Host tissue fluids absorbed directly
- Organisms
- Cuscuta (Amarbel), tapeworm, roundworm, ticks, leeches
3The Human Alimentary Canal and Digestive Enzymes
Human Digestive Enzymes & Biochemical Reactions
| Digestive Organ | Juice / Secretion | Active Enzyme | Substrate & Action | Product Formed |
|---|---|---|---|---|
| Mouth (Oral cavity) | Saliva (Salivary glands) | Salivary Amylase (Ptyalin) | Breaks complex starch (pH 6.8) | Maltose (simple disaccharide sugar) |
| Stomach | Gastric juice (Gastric glands) | Pepsin (activated by HCl, pH 1.5) | Digests complex proteins | Peptones and Proteoses |
| Small Intestine (Liver) | Bile juice (stored in gall bladder) | No enzymes (Bile salts) | Emulsifies large fat globules into tiny droplets | Emulsified fat droplets + alkaline medium |
| Small Intestine (Pancreas) | Pancreatic juice | Trypsin, Amylase, Lipase | Trypsin digests proteins; Lipase digests emulsified fats | Peptides, Maltose, Fatty acids + Glycerol |
| Small Intestine (Ileum) | Intestinal juice (Succus entericus) | Peptidases, Maltase, Intestinal Lipase | Complete final digestion | Amino acids, Glucose, Fatty acids + Glycerol |
Mouth (Oral cavity)
- Juice / Secretion
- Saliva (Salivary glands)
- Active Enzyme
- Salivary Amylase (Ptyalin)
- Substrate & Action
- Breaks complex starch (pH 6.8)
- Product Formed
- Maltose (simple disaccharide sugar)
Stomach
- Juice / Secretion
- Gastric juice (Gastric glands)
- Active Enzyme
- Pepsin (activated by HCl, pH 1.5)
- Substrate & Action
- Digests complex proteins
- Product Formed
- Peptones and Proteoses
Small Intestine (Liver)
- Juice / Secretion
- Bile juice (stored in gall bladder)
- Active Enzyme
- No enzymes (Bile salts)
- Substrate & Action
- Emulsifies large fat globules into tiny droplets
- Product Formed
- Emulsified fat droplets + alkaline medium
Small Intestine (Pancreas)
- Juice / Secretion
- Pancreatic juice
- Active Enzyme
- Trypsin, Amylase, Lipase
- Substrate & Action
- Trypsin digests proteins; Lipase digests emulsified fats
- Product Formed
- Peptides, Maltose, Fatty acids + Glycerol
Small Intestine (Ileum)
- Juice / Secretion
- Intestinal juice (Succus entericus)
- Active Enzyme
- Peptidases, Maltase, Intestinal Lipase
- Substrate & Action
- Complete final digestion
- Product Formed
- Amino acids, Glucose, Fatty acids + Glycerol
4Exam Corner: Tips, Mistakes & Board Questions
Critical Board Exam High-Yield Points
- Hydrochloric acid (HCl) in gastric juice creates an acidic medium (pH ~1.5) necessary for pepsin activation and kills ingested pathogens. Mucus protects stomach lining from self-digestion.
- Bile juice contains no digestive enzymes yet is vital for digestion because: (1) It makes acidic food from stomach alkaline so pancreatic enzymes can work, and (2) Bile salts emulsify large fat globules.
- Villi are millions of tiny finger-like projections in the inner lining of the small intestine that increase surface area for rapid absorption of digested nutrients into blood capillaries.
Exam question · CBSE Class 10 Board
What is the role of bile juice in human digestion, considering it contains no enzymes?
- A.It digests proteins into amino acids
- B.It makes acidic chyme alkaline and emulsifies fats into small droplets for lipase action
- C.It breaks starch into glucose
- D.It acts solely as an excretory waste product
- Bile juice secreted by the liver performs two crucial non-enzymatic functions:
- 1. Neutralization: Its alkaline salts convert acidic food from stomach into alkaline medium, enabling pancreatic enzymes to act.
- 2. Emulsification: Bile salts break down large fat globules into tiny droplets, dramatically increasing surface area for lipase enzyme action.
- Correct answer is option B.
Answer: B. It makes acidic chyme alkaline and emulsifies fats into small droplets for lipase action
Remember
- Photosynthesis convertsCO₂ and H₂O into Glucose and O₂using light energy.
- Stomata open when guard cells becometurgidand close whenflaccid.
- Small intestine is the site ofcomplete digestionand absorption viavilli.
- Bile juice contains no enzymes, but is essential forfat emulsification
Check yourself
Question 1
Which component of gastric juice protects the inner mucosal lining of the stomach from the corrosive action of hydrochloric acid?