Respiration & Energy
Respiration & Energy – Life Processes
Cellular respiration and types of respiration
Core idea: Cellular respiration is the process by which cells break down food (usually glucose) to release usable energy in the form of ATP. It happens in almost every living cell.
| Concept | What happens in the cell | Key exam point |
|---|---|---|
| Cellular respiration | Glucose is gradually broken down with or without oxygen and energy is captured as ATP. | Occurs in all living cells; major steps inside mitochondria (called “power house of the cell”). |
| ATP (Adenosine Triphosphate) | High-energy molecule; energy currency of the cell. | Energy from respiration is stored in ATP and released when ATP → ADP + Pi. |
| Heat production | Some energy from respiration appears as heat. | Explains why our body remains warm and why germinating seeds show rise in temperature. |
Types of respiration:
| Type | Oxygen use | End products | Energy yield | Examples |
|---|---|---|---|---|
| Aerobic respiration | Uses oxygen | Carbon dioxide + water + energy | High energy (maximum ATP) | Most cells of plants and animals, including human muscle at rest. |
| Anaerobic respiration (in yeast) | No oxygen | Alcohol + carbon dioxide + little energy | Low energy (few ATP) | Yeast used in baking and brewing. |
| Anaerobic respiration (in animal muscles) | Insufficient oxygen (during intense exercise) | Lactic acid + little energy | Low energy, muscle fatigue | Human leg muscles during fast running, heavy exercise. |
Word equation for aerobic respiration:
Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP + heat)
Respiration in plants and respiration in animals
Respiration in plants: Plants also respire all the time (day and night). They take in oxygen and give out carbon dioxide through different structures.
| Plant part | Structure for gas exchange | How gases move |
|---|---|---|
| Leaves | Stomata (tiny pores mostly on underside of leaf) | O₂ enters and CO₂ leaves by diffusion; guard cells control opening and closing. |
| Stems | Lenticels (small openings in woody stems) or thin epidermis in herbaceous stems | Diffusion of gases with air outside. |
| Roots | Root hairs | Oxygen from air trapped between soil particles diffuses into root hairs; CO₂ diffuses out. |
Respiration in animals: Animals have specialised organs for breathing and gaseous exchange, but cellular respiration is similar (food + O₂ → CO₂ + H₂O + energy).
| Animal group | Main respiratory organ | Example |
|---|---|---|
| Terrestrial vertebrates | Lungs | Human, cow, dog, birds. |
| Fish | Gills | Rohu, catla, other bony fishes. |
| Insects | Tracheal system (air tubes) | Grasshopper, cockroach. |
| Amphibians (in water and on land) | Skin and lungs (adult); gills (tadpoles) | Frog. |
Human respiratory system (basic flow):
Nostrils → Nasal cavity → Trachea (windpipe) → Bronchi → Bronchioles → Alveoli (air sacs in lungs).
| Part | Function | Exam point |
|---|---|---|
| Nasal cavity | Filters, warms and moistens the air. | Hair and mucus trap dust and germs. |
| Alveoli | Site of gas exchange between air and blood. | Large surface area, thin walls, rich blood supply. |
| Diaphragm and intercostal muscles | Help in breathing movements (inspiration and expiration). | During inspiration, diaphragm moves down and chest cavity expands. |
Respiration versus combustion
Combustion is burning of substances with oxygen to release heat and light. Respiration is a controlled release of energy from food inside cells. Both involve oxidation, but they are not the same.
| Feature | Respiration | Combustion |
|---|---|---|
| Where it occurs | Inside living cells (biological process). | Outside body, in engines, stoves, candles etc. |
| Speed of reaction | Slow and step-wise. | Fast and often violent. |
| Energy release | Stored in ATP; only part released as heat. | Released mainly as heat and light, no ATP formed. |
| Temperature change | Mild rise in body/seed temperature. | High temperature, flame often visible. |
| Control | Controlled by enzymes. | Not controlled by enzymes; difficult to regulate fine steps. |
| End products | CO₂, H₂O, energy (ATP + heat). | CO₂, H₂O, and heat/light; sometimes harmful gases and smoke. |
Common link: Both use oxygen and both release carbon dioxide and energy. But respiration is life process, combustion is purely physical/chemical burning.
Photosynthesis versus respiration
Photosynthesis and respiration are opposite in many ways, but are linked in the energy cycle of living organisms.
| Aspect | Photosynthesis | Respiration |
|---|---|---|
| Basic role | Process of food making (energy storage). | Process of food breakdown (energy release). |
| Where it occurs | Chloroplasts (green parts of plant with chlorophyll). | All living cells; main steps in mitochondria. |
| Raw materials | CO₂ + H₂O (in presence of sunlight and chlorophyll). | Food (glucose) + O₂. |
| End products | Glucose + O₂ + water (as by-product). | CO₂ + H₂O + energy (ATP + heat). |
| Energy | Light energy from sun is trapped and stored in chemical bonds of glucose. | Chemical energy of glucose is released and stored in ATP. |
| Gas exchange | CO₂ is used, O₂ is released. | O₂ is used, CO₂ is released. |
| Time of occurrence | Only in light (daytime or artificial light) in green parts. | All the time, day and night in all living cells. |
Simple word equations:
Photosynthesis: Carbon dioxide + Water → Glucose + Oxygen (in presence of light and chlorophyll).
Respiration: Glucose + Oxygen → Carbon dioxide + Water + Energy.