Animal digestion and absorption

Recall how tissues form an organ

Food in the gut is not yet absorbed into the body

Food contains substances needed by the body; many nutrient molecules are too large to absorb until digestion breaks them into smaller molecules

Physical breakdown changes food-piece size; chemical digestion changes large nutrient molecules into smaller molecules

Absorption is transfer across the gut lining into the body; a substance inside the gut cavity has not necessarily crossed that lining

This topic uses a simplified human system as an animal example; other animals can have different digestive arrangements

Separate food pieces from molecules

Teeth physically break food into smaller pieces, exposing more surface; this action alone does not turn every large nutrient molecule into a smaller molecule

Digestive enzymes help break particular large molecules into smaller molecules; for example, enzymes can split starch into smaller sugars

Chewing and enzyme action can occur together, but they are not the same process; identify the specific action described in a question

Classify a change in food-piece size

Classify a change in nutrient molecules

Follow a continuous food passage

The liver and pancreas help digestion by supplying substances to the gut, but swallowed food does not pass through those organs

The tract's muscular waves are called peristalsis; they move contents without requiring every nutrient molecule to change in that movement step

Match muscular waves with their direct role

Coordinated waves of muscle contraction move food along the oesophagus towards the stomach

This movement is called peristalsis

What is the immediate function of the described muscle action?

The contraction waves move digestive contents along the tract; the record describes transport, not complete chemical digestion or lung gas exchange

Moving contents along the digestive tract

Keep assisting organs separate from the food passage

Connect the intestine surface with nutrient transfer

The small intestine is an organ with several tissues; muscle tissue moves its contents, while specialised lining tissue supports absorption

Folds and finger-like villi increase the lining's surface area; tiny projections on the lining cells increase it further

A villus is a multi-cellular projection of tissue, not one single specialised cell

A thin lining and nearby blood vessels provide a short transfer distance for substances such as glucose; blood flow carries absorbed glucose away to other body regions

Not all absorbed nutrients first enter the same vessels; this introductory route follows glucose entering blood, while much absorbed fat first enters lymph vessels

Explain why more surface can support absorption

Connect a thin barrier to transfer distance

A villus has a thin surface layer, with small blood vessels close beneath it

Glucose crosses this lining into the blood

Which structure-function explanation fits this record?

The thin lining and nearby vessels provide a short transfer distance for glucose; absorption moves molecules rather than turning them into cells

A thin barrier gives glucose a short distance to cross into nearby blood vessels

Separate digestion from absorption

Keep water absorption and egestion distinct

Water is absorbed in both the small intestine and large intestine; do not turn the large intestine's important water role into a claim that no water is absorbed earlier

Removing water from the remaining contents makes them less watery; it does not change every undigested substance into glucose

Egestion is removal of material that remained in the gut, as faeces; it is different from absorption across the lining

Excretion removes metabolic wastes made by cells, such as carbon dioxide through the lungs; not every process that removes unwanted material has the same name

Retain both water-absorption sites

Track material that was not absorbed

G means gut cavity, B blood, C body cells and E expelled faeces; compare the route of absorbed glucose with the unabsorbed remainder; arrows summarise transfer, not anatomy, travel speed or the path of every nutrient

In the absorbed-glucose route, which process is represented by G to B?

Follow glucose from the gut to a working cell

Digestion makes small nutrient molecules available; absorption moves glucose across the intestine lining; the circulatory system then distributes absorbed glucose to body cells

Cells can use glucose in respiration, making stored energy available for their activities; digestion in the gut is not the same as respiration in cells

The digestive system cannot by itself deliver every nutrient to every distant cell; it cooperates with transport and other systems

A change to working absorption surface directly affects absorption capacity; do not claim that enzymes or muscle action have also stopped if the record says they still work

Link absorption with supply to muscle cells

Identify the direct effect of reduced absorption surface

Explain a complete nutrient route

Written and drawing task for discussion, not automatic marking: a meal contains starch; enzymes break it down to small sugars including glucose, which can be absorbed

Draw and explain a route from food in the digestive tract to glucose reaching a muscle cell; distinguish physical breakdown, chemical digestion, absorption and blood transport

Include one feature of the intestine lining that supports absorption, and predict the direct effect of less working villus surface while digestion and movement remain possible

Check each process and its location

Model: chewing reduces food-piece size; digestive enzymes break starch into smaller sugars, including glucose, in the gut; glucose crosses the small intestine lining into the blood; blood carries it towards working muscle cells

Folds and villi provide more surface for absorption, and the thin lining provides a short transfer distance to nearby blood vessels

If digestion and movement remain possible, less working villus surface directly reduces absorption capacity; do not describe digestion or movement as completely stopped

The whole route links different tissues within organs and different organ systems within one organism; it does not place a tiny stomach inside each muscle cell

Connect organisation with digestion and survival

Keep food pieces, nutrient molecules and whole organs separate when naming a process

Distinguish physical breakdown, chemical digestion, movement, absorption and egestion; the digestive organs cooperate but do not all perform the same job

Explain how specialised lining structures support absorption and how blood transport connects absorbed nutrients with cells elsewhere in the organism