Transport & Excretion
Transport & Excretion – Plants and Animals
Human Circulatory System – Blood, Vessels and Heart
Core idea: The human circulatory system transports oxygen, food, hormones, waste materials to and from different parts of the body using blood, blood vessels and heart.
| Component | Structure | Main Function |
|---|---|---|
| Blood | Fluid connective tissue with plasma, RBCs, WBCs and platelets. | Transports gases, nutrients, hormones, waste and helps in defence and clotting. |
| Blood vessels | Network of arteries, veins and capillaries. | Provide pathways for blood circulation to every cell. |
| Heart | Muscular pumping organ with four chambers. | Pumps blood to lungs and rest of body by rhythmic contractions. |
Types of blood vessels:
| Vessel | Direction of flow | Features | Exam hint |
|---|---|---|---|
| Arteries | Carry blood away from heart. | Thick, elastic walls; usually carry oxygenated blood (except pulmonary artery). | High pressure, blood spurts when cut. |
| Veins | Carry blood towards heart. | Thin walls, wide lumen, have valves; usually carry deoxygenated blood (except pulmonary vein). | Low pressure, slow flow, dark red colour. |
| Capillaries | Connect arteries and veins. | Very thin, one-cell-thick walls, numerous and narrow. | Site of exchange of materials between blood and tissues. |
Structure of human heart (four-chambered):
- Right atrium – receives deoxygenated blood from body (via vena cavae).
- Right ventricle – pumps deoxygenated blood to lungs (via pulmonary artery).
- Left atrium – receives oxygenated blood from lungs (via pulmonary veins).
- Left ventricle – pumps oxygenated blood to body (via aorta), strongest chamber.
Double circulation in humans:
| Loop | Path | Purpose |
|---|---|---|
| Pulmonary circulation | Right ventricle → lungs → left atrium. | Exchanges CO₂ for O₂ in lungs. |
| Systemic circulation | Left ventricle → body tissues → right atrium. | Supplies O₂ and nutrients, collects CO₂ and wastes. |
Memory Line: “Right = impure (to lungs), Left = pure (to body)” – Right heart deals mainly with deoxygenated blood, left heart with oxygenated blood.
Exam Tip: If a question asks “which artery carries deoxygenated blood?” → answer is pulmonary artery. If it asks “which vein carries oxygenated blood?” → answer is pulmonary vein.
Evolution of Transport System in Animals
Key idea: As animals increased in size and complexity, simple diffusion was not enough. Transport systems evolved from very simple to highly organised circulatory systems.
| Level of organism | Example | Transport method | Reason / Feature |
|---|---|---|---|
| Unicellular | Amoeba, Paramecium | Simple diffusion through cell surface. | Small size, large surface area; every part close to environment. |
| Simple multicellular (no specialised vessels) | Flatworms (Planaria), sponges | Diffusion through body surface + body cavity fluids. | Thin body, many cells directly in contact with environment or cavity. |
| Open circulatory system | Many arthropods (cockroach, grasshopper) | Blood (haemolymph) pumped into open spaces (sinuses); directly bathes organs. | No distinct capillary network; pressure low, circulation slow but sufficient for small animals. |
| Closed circulatory system (simple) | Earthworm, some molluscs | Blood flows in closed tubes (vessels); exchange via capillaries. | Better control of pressure and direction; more efficient transport. |
| Closed with single circulation | Bony fish | Heart → gills → body → back to heart (single loop). | Two-chambered heart; blood passes gills only once before body. |
| Closed with double circulation (partial) | Amphibians, most reptiles (3-chambered heart) | Some mixing of oxygenated and deoxygenated blood. | Intermediate efficiency; adapted to both water and land life in amphibians. |
| Closed with double circulation (complete) | Birds and mammals (including humans) | Separate pulmonary and systemic circuits; no blood mixing. | Four-chambered heart; supports high metabolic rate and constant body temperature. |
Memory Line: “Simple diffusion → open → closed single → closed double” – Think of increasing efficiency step-by-step as animals become more active.
Exam Tip: Single circulation → seen in fish (2 chambers). Double circulation complete → seen in birds and mammals (4 chambers). Expect match-the-following or column questions on this.
Transportation in Plants – Water, Minerals and Food
Key idea: Plants do not have a heart, but they have a vascular system made of xylem and phloem to transport water, minerals and prepared food.
| Tissue | What it carries | Direction of flow | Source → Destination |
|---|---|---|---|
| Xylem | Water and dissolved minerals. | Mostly upward (roots → leaves). | Roots → stem → branches → leaves (transpiration stream). |
| Phloem | Prepared food (mainly sucrose) and some hormones. | Both upward and downward (bi-directional). | Leaves (source) → growing parts, roots, fruits, storage organs (sink). |
Uptake and movement of water in plants (xylem):
- Root hairs absorb water and minerals from soil by osmosis and diffusion.
- Water moves from cell to cell across root cortex → xylem of root → xylem of stem → xylem of leaves.
- Transpiration (evaporation of water from stomata of leaves) pulls water column upward – transpirational pull.
- Cohesion and adhesion of water molecules help maintain unbroken water column in xylem vessels.
Transport of food in plants (phloem – translocation):
- Food is prepared in leaves by photosynthesis and loaded into phloem sieve tubes.
- Transport is from regions of high concentration (source) to low concentration (sink).
- Energy from ATP is used to load food into phloem – active transport.
- Transport can be upwards (to fruits, buds) or downwards (to roots, storage organs).
| Process | Role in plants | Associated tissue |
|---|---|---|
| Transpiration | Cools leaves, helps in water and mineral ascent. | Xylem. |
| Translocation | Distribution of food from leaves to all parts. | Phloem. |
Memory Line: “Xylem rises, Phloem flows” – Xylem mainly upward, phloem in all directions from source to sink.
Exam Tip: If a question mentions “girdling experiment” (removing a ring of bark) and food not reaching roots → answer must involve phloem getting cut, not xylem.
Excretion – Humans, Other Organisms and Plants
Excretion is the process of removal of metabolic waste products produced inside the body such as urea, uric acid, carbon dioxide, excess salts, water. It is essential to maintain internal balance (homeostasis).
Excretion in Human Beings – Human Excretory System
Main organs: Two kidneys, two ureters, urinary bladder, urethra.
| Part | Structure | Function |
|---|---|---|
| Kidneys | Bean-shaped organs on either side of vertebral column in abdomen. | Filter blood, remove urea, adjust water and salt balance, form urine. |
| Ureter | Muscular tube from each kidney to urinary bladder. | Transports urine by peristaltic movements. |
| Urinary bladder | Elastic muscular sac. | Stores urine temporarily. |
| Urethra | Opening from bladder to outside. | Releases urine from body by micturition. |
Nephron – functional unit of kidney:
- Bowman’s capsule – cup-shaped, surrounds a capillary knot called glomerulus.
- Glomerular filtration – blood under pressure filters water, urea, salts and small molecules into Bowman’s capsule (forms glomerular filtrate).
- Tubular reabsorption – useful substances (glucose, amino acids, some water, ions) are reabsorbed back into blood from tubule.
- Tubular secretion – some extra ions and wastes are secreted from blood into tubule.
- Final fluid in collecting duct is urine (mainly water + urea + salts).
Excretion in Other Organisms
| Organism | Excretory structure | Main waste and method |
|---|---|---|
| Amoeba (unicellular) | Contractile vacuole. | Collects excess water and waste; periodically contracts and expels them out. |
| Earthworm | Nephridia (segmental excretory organs). | Remove nitrogenous wastes from body fluid and release outside through pores. |
| Insects (e.g., cockroach) | Malpighian tubules. | Remove uric acid and other wastes from haemolymph into gut; excreted with faeces. |
| Fish | Kidneys and gills. | Excrete ammonia mainly through gills; kidneys remove other wastes. |
Excretion and Release of Substances in Plants
Plants produce fewer toxic wastes and have no special excretory organs, but they remove or store wastes by different methods:
- Gaseous wastes – CO₂ and O₂ leave through stomata and lenticels by diffusion.
- Excess water – lost by transpiration and guttation.
- Organic wastes – often converted into resins, gums, latex, essential oils and stored in special cells or ducts (e.g., rubber latex, pine resin).
- Waste storage in leaves – some wastes are stored in leaves, bark or fruits, which later fall off (leaf fall serves as excretory mechanism).
Excretion vs Secretion
| Feature | Excretion | Secretion |
|---|---|---|
| Definition | Removal of metabolic waste products from body. | Release of useful substances produced by cells. |
| Examples | Urea in urine, CO₂ in exhaled air, sweat. | Saliva, hormones, enzymes, mucus, digestive juices. |
| Purpose | Maintain internal chemical balance and prevent toxicity. | Help in digestion, regulation, lubrication and other body functions. |
| Organs/glands | Kidneys, lungs, skin etc. | Salivary glands, endocrine glands, gastric glands, pancreas etc. |
Memory Line: “Excretion throws waste out; secretion sends useful things out.” – Both are release processes, but their products and purposes are different.
Exam Tip: Questions often confuse sweat (mainly excretory – removes water, salts, some urea) with saliva (secretory – contains enzyme salivary amylase). Check whether the substance is waste or useful.