Campbell Biology Chapter 41 Review: Animal Nutrition

41.1 What a diet has to supply

pp. 875–880

On the AP exam? Background

Vitamins, minerals and deficiency diseases aren't in the current course. What is tested: living things take in carbon and nitrogen to build their molecules (Topic 1.2), and taking in less energy than you use leads to loss of body mass (Topic 8.2).

In the course: Topic 1.2 Elements of Life, Topic 1.5 Lipids, Topic 1.7 Proteins, Topic 8.2 Energy Flow Through Ecosystems (notes, videos and more questions)

Key points

Food does three jobs. It's fuel for making ATP, it supplies carbon and nitrogen in organic form for building new molecules, and it delivers essential nutrients the body can't make.
An essential nutrient is something your cells need but can't build, so it has to arrive ready-made in food. What counts as essential depends on the species: one animal may make a molecule that another must eat.
Essential nutrients fall into four groups: vitamins, minerals, and the amino acids and fatty acids an animal can't make for itself. Humans need 9 essential amino acids (older books say 8 for adults), plus a few unsaturated fatty acids such as linoleic acid.
Vitamins are organic molecules needed in tiny amounts, often because they become coenzymes that are used again and again. Water-soluble ones (the B vitamins and C) mostly leave in urine, while fat-soluble ones (A, D, E and K) build up in fat, so megadoses can be toxic.
Minerals are inorganic elements such as calcium, iron, iodine and sodium. They build bone, carry oxygen in hemoglobin, help enzymes work and keep nerves firing. Too much can cause harm as well as too little.
Malnutrition comes in two forms: a diet short on some essential nutrient, or getting too little energy overall (undernutrition). Without enough food energy, the body spends its reserves in order: glycogen, then fat, and eventually protein from muscles and organs.
Researchers can't run harmful diet experiments on people, so they learn about human needs from inherited disorders that affect nutrients and from epidemiology, which compares health across large groups.

Key terms (15)

herbivore: An animal that eats mostly plants or algae, like a rabbit or a grasshopper.
carnivore: An animal that eats mostly other animals, like a wolf or an owl.
omnivore: An animal that regularly eats both plants and animals, like you, a raccoon or a pig.
essential nutrient: Something your cells need but can't make, so it has to come ready-made in food.
essential amino acid: An amino acid an animal can't build and must get from protein in its diet. Humans have 9 of them.
complete protein: A food protein that supplies every essential amino acid in useful amounts, like the protein in fish or soy.
essential fatty acid: A fatty acid with double bonds in its chain that an animal can't make and has to eat, such as linoleic acid in humans.
vitamin: An organic molecule you need in tiny amounts, often because it becomes part of a coenzyme that gets reused.
water-soluble vitamin: A vitamin that dissolves in water, like vitamin C and the B vitamins. Extra is mostly lost in urine.
fat-soluble vitamin: A vitamin that dissolves in fat, like A, D, E and K. Extra gets stored in fat and the liver, so too much can build up.
mineral: An inorganic nutrient, such as calcium, iron or iodine, needed for jobs like building bone or carrying oxygen.
coenzyme: A small organic helper molecule that an enzyme needs in order to work. Many are made from vitamins.
malnutrition: Poor health caused by a diet that's missing essential nutrients or doesn't supply enough energy.
undernutrition: Not getting enough food energy. The body burns its stores and eventually its own proteins.
epidemiology: The study of health and disease across whole populations, often by comparing groups of people.

Check yourself: 41.1 What a diet has to supply

4 questions on 41.1 What a diet has to supply. Pick an answer to see if you got it, and why.

Question 1 of 4

Which statement best defines an essential nutrient for an animal?

Question 2 of 4

Cats fed for months on a diet with no taurine, a small sulfur-containing compound, develop heart and eye damage. Dogs fed the same diet stay healthy. Which explanation best fits these results?

Question 3 of 4

Young rats are fed a diet with plenty of calories in which the only protein is gelatin. Gelatin contains no tryptophan, one of the amino acids rats can't make. The rats soon stop growing. What best explains this?

Question 4 of 4

Two people take supplements at about 20 times the recommended amount every day for a year. One takes vitamin A and the other takes vitamin C. Who is more likely to build up toxic levels, and why?

0 of 4 answered

41.2 From eating to elimination

pp. 880–883

On the AP exam? Background

The four stages and the feeding types aren't named in the current course. The tested ideas underneath are hydrolysis (Topic 1.3), lysosomes and compartments that keep enzymes contained (Topics 2.1 and 2.9) and taking in food by endocytosis (Topic 2.5).

In the course: Topic 1.3 Introduction to Macromolecules, Topic 2.1 Cell Structure and Function, Topic 2.5 Membrane Transport, Topic 2.9 Cell Compartmentalization (notes, videos and more questions)

Key points

Processing food takes four steps: ingestion (taking it in), digestion (breaking it down), absorption (cells taking up the small pieces) and elimination (getting rid of what's left).
Animals get food in different ways. Suspension and filter feeders strain small particles out of water, substrate feeders live in or on what they eat, fluid feeders suck up liquids like nectar or blood, and bulk feeders, like you, eat big chunks.
Chewing and churning tear food into bits without changing its molecules. Every cut exposes fresh surface, so enzymes can reach much more of the food at once.
Chemical digestion is hydrolysis: enzymes add water to split polymers into monomers. Starch becomes sugars, proteins become amino acids, nucleic acids become nucleotides and fats become fatty acids and glycerol. The animal then rebuilds its own molecules from those parts.
Digestive enzymes would attack the animal's own cells, so digestion happens inside compartments. In intracellular digestion, a cell engulfs food by endocytosis, and a lysosome fuses with the resulting food vacuole.
Most animals digest at least partly outside their cells, in a space connected to the outside world. A gastrovascular cavity has one opening that works as both mouth and anus; an alimentary canal is a tube with a mouth at one end and an anus at the other.
Because food in a two-opening tube only moves forward, different stretches can take on different jobs (storage, grinding, enzyme action, absorption), and the animal can start a new meal while an earlier one is still moving through.

Key terms (15)

ingestion: Taking food into the body: the act of eating.
digestion: Splitting the large molecules in food into units small enough to cross into the body's cells.
absorption: Cells taking up the small molecules that digestion produces.
elimination: Getting rid of the undigested leftovers as feces.
mechanical digestion: Breaking food apart physically, by chewing or churning, without breaking chemical bonds. It exposes more surface to enzymes.
enzymatic hydrolysis: Using enzymes to split polymers into monomers by adding water across the bonds.
suspension feeder: An animal that eats tiny bits of food floating in water, often by straining them out.
substrate feeder: An animal that makes its home inside or on top of its food supply and eats its way through it.
fluid feeder: An animal that feeds by drinking liquid from another living thing, such as nectar, plant sap or blood.
bulk feeder: An animal that takes in sizable chunks of food by biting, tearing or swallowing whole. This is how you eat.
food vacuole: A membrane sac holding food that a cell has engulfed. Enzymes arrive when a lysosome fuses with it.
intracellular digestion: Breaking food down inside a cell, within a food vacuole.
extracellular digestion: Digestion carried out in a gut cavity, where enzymes are released onto the food, rather than inside individual cells.
gastrovascular cavity: A digestive sac with one opening that serves as both mouth and anus. It also spreads nutrients around the body.
alimentary canal: A digestive tube that runs from mouth to anus, so food moves through it in one direction.

Check yourself: 41.2 From eating to elimination

4 questions on 41.2 From eating to elimination. Pick an answer to see if you got it, and why.

Question 1 of 4

Larvae of a certain beetle hatch inside a fallen log and spend months chewing tunnels through the wood around them, eating as they go. Which feeding category fits these larvae best?

Question 2 of 4

A polypeptide made of 150 amino acids is completely digested into free amino acids. How many water molecules are used up?

Question 3 of 4

A heron eats frogs, yet frog proteins are never found intact in the heron's tissues, even though the heron builds its own proteins from what it eats. What best explains this?

Question 4 of 4

An amoeba engulfs bacteria by phagocytosis. A mutation stops its lysosomes from fusing with the vesicles that hold the engulfed bacteria. What is the most likely result?

0 of 4 answered

41.3 A tour of the human digestive system

pp. 883–889

On the AP exam? Background

You won't be asked to name digestive organs or enzymes. This system is a common setting for tested ideas, though: villi and surface area (Topic 2.2), passive and active transport (Topics 2.5 and 2.8), water following ions by osmosis (Topic 2.7), pH and enzyme activity (Topic 3.2) and positive feedback (Topic 4.4).

In the course: Topic 2.2 Cell Size, Topic 2.5 Membrane Transport, Topic 2.7 Tonicity and Osmoregulation, Topic 2.8 Mechanisms of Transport, Topic 3.2 Environmental Impacts on Enzyme Function, Topic 4.4 Feedback (notes, videos and more questions)

Key points

The mammalian system is an alimentary canal plus helper glands (salivary glands, pancreas, liver and gallbladder) that send their secretions in through ducts. Waves of smooth-muscle contraction called peristalsis push food along, and rings of muscle called sphincters act as gates between sections.
In the mouth, teeth break food up, amylase in saliva starts splitting starch, and mucus keeps everything slippery. When you swallow, the epiglottis folds over the entrance to the airway so food goes down the esophagus and not the trachea.
The stomach holds a meal, churns it into chyme and begins breaking down protein. Its gland cells pump out H⁺ and Cl⁻, making acid near pH 2 that unfolds food proteins. Pepsin is released as inactive pepsinogen; acid starts converting it, and active pepsin then converts more of it, a case of positive feedback. A mucus coat and constant renewal of lining cells keep the stomach from digesting itself.
Most digestion happens in the duodenum, the first part of the small intestine. The pancreas adds bicarbonate to neutralize acid, plus enzymes such as trypsin and lipase. Bile from the liver, stored in the gallbladder, breaks fat into tiny droplets, and enzymes attached to the intestinal lining finish the job.
The rest of the small intestine absorbs. Folds, villi and microvilli give it an enormous surface. Some nutrients cross by facilitated diffusion and others by active transport against their gradient. Blood leaving the intestine reaches the liver first, through the hepatic portal vein, so the liver gets first pick: it evens out nutrient levels and breaks down many foreign or toxic molecules before blood reaches the rest of the body.
Fat goes a different way. Lipase frees fatty acids and monoglycerides, which slip into the lining cells. There they are joined back into triglycerides, wrapped in protein-coated particles called chylomicrons and released into lacteals, the lymph vessels inside each villus.
In the colon, cells move salts out of the gut contents and water follows by osmosis, which is why feces firm up as they travel. The colon is also home to trillions of bacteria (your gut microbiome) that ferment leftovers and supply a bit of vitamin K and some B vitamins. The rectum stores feces until they leave through the anus.

Key terms (15)

peristalsis: Rhythmic squeezes of the smooth muscle in the gut wall that push food forward, a bit like squeezing toothpaste along a tube.
sphincter: A ring of muscle that works like a gate between two sections of the gut.
salivary amylase: An enzyme in saliva that starts breaking starch into shorter sugar chains.
epiglottis: The flexible lid at the top of the windpipe that tips down during swallowing, steering food into the esophagus.
chyme: The soupy, acidic mix of partly digested food and gastric juice that leaves your stomach.
pepsin: The stomach's main protease. Its optimum is around pH 2, far lower than that of most enzymes.
pepsinogen: The inactive form of pepsin. Acid, and then pepsin itself, switch it on once it's in the stomach cavity.
duodenum: The first short section of the small intestine, where chyme meets bicarbonate, enzymes and bile poured in from nearby organs.
bile: A liquid made by the liver and stored in the gallbladder. Its bile salts break fat into tiny droplets, but it contains no enzymes.
villi: Finger-like projections lining the small intestine that greatly expand its absorbing surface.
microvilli: Tiny projections on each cell lining the intestine. Together they form a brush border that adds even more surface.
hepatic portal vein: The vessel that carries nutrient-rich blood from the intestines straight to the liver.
chylomicron: A tiny lipid-and-protein particle that intestinal cells build around absorbed fat so it can travel in watery lymph and blood.
lacteal: A small lymph vessel in the center of each villus that takes up chylomicrons.
colon: The main part of the large intestine. It reabsorbs water and houses most of your gut bacteria.

Check yourself: 41.3 A tour of the human digestive system

4 questions on 41.3 A tour of the human digestive system. Pick an answer to see if you got it, and why.

Question 1 of 4

Activity of two protein-digesting enzymes was measured at different pH values, as a percent of each enzyme's maximum (invented data). pH | Pepsin | Trypsin 2 | 96 | 4 4 | 58 | 12 6 | 10 | 61 8 | 2 | 97 A person's pancreas releases too little bicarbonate, so chyme in the duodenum stays near pH 3. Based on the data, what is most likely?

Question 2 of 4

A small amount of active pepsin is added to a solution of pepsinogen at pH 2. Over time, the amount of active pepsin rises slowly at first and then faster and faster. What best explains this pattern?

Question 3 of 4

In untreated celiac disease, an immune reaction to gluten flattens the villi lining the small intestine. The pancreas still releases its enzymes, and bile still reaches the intestine. Which problem is most likely?

Question 4 of 4

Cells lining the small intestine keep taking in glucose from the lumen even when glucose is more concentrated inside them than in the lumen. The uptake stops when a drug blocks the Na⁺/K⁺ pumps on the side of the cells facing the blood. What best explains these results?

0 of 4 answered

41.4 Digestive systems shaped by diet

pp. 889–891

On the AP exam? Background

Teeth, gut length and stomach chambers aren't in the current course. The tested ideas here are mutualism (Topic 8.5), natural selection fitting traits to a diet (Topic 7.2), microbes that ferment food (Topic 3.5) and why cellulose is hard to digest (Topic 1.4).

In the course: Topic 7.2 Natural Selection, Topic 8.5 Community Ecology, Topic 3.5 Cellular Respiration, Topic 1.4 Carbohydrates (notes, videos and more questions)

Key points

Vertebrate digestive systems share one basic plan, but natural selection has tuned the parts to each animal's diet.
Teeth show this well. Meat-eaters tend to have sharp canines and blade-like cheek teeth that slice, plant-eaters have wide grinding cheek teeth, and omnivores like you have a mix of incisors, canines, premolars and molars.
Animals that catch big meals only now and then, such as many predators, often have a stomach that can stretch to hold a huge amount at once.
For animals of similar size, gut length tracks diet: leaf- and grass-eaters tend to have much longer guts than meat-eaters. Plant food is wrapped in tough cell walls, and a long gut keeps it inside longer and offers more lining for absorption.
Vertebrates have no enzyme of their own for cellulose. Plant-eaters solve this by housing bacteria, archaea and protists in a gut chamber where the microbes ferment plant fiber into compounds the host can absorb, often making vitamins and amino acids for the host along the way.
Where fermentation happens varies. Ruminants such as goats, giraffes and antelope ferment food in a stomach with several chambers, chew it again as cud, and later digest many of the microbes themselves. Others use a large cecum after the small intestine, and some of these eat part of their feces to recover nutrients the microbes made.
Partnering with microbes shows up again and again across the animal kingdom, from insects to mammals, wherever an animal lives on food it can't fully break down alone.

Key terms (13)

dentition: An animal's set of teeth: how many it has and what shapes they are.
incisor: A flat, chisel-like front tooth used for biting and cutting.
canine: A pointed tooth beside the incisors, used for gripping and tearing. It's long in many meat-eaters.
premolar: A cheek tooth between the canines and molars, used for crushing or shearing.
molar: A broad tooth at the back of the jaw for grinding. It's especially wide and ridged in plant-eaters.
cellulose: The tough glucose polymer in plant cell walls. No vertebrate makes an enzyme that can digest it.
fermentation chamber: A part of the gut where microbes break down food the animal can't digest on its own.
cecum: A pouch where the small and large intestines meet. It's large in many plant-eaters and holds fermenting microbes.
mutualism: A relationship between two species in which both benefit, like gut microbes and the animals that house them.
ruminant: A hoofed mammal, such as a goat or a giraffe, whose stomach has several chambers where microbes ferment plant food.
rumen: The largest chamber of a ruminant's stomach, packed with microbes that ferment plant material.
cud: Partly fermented plant material that a ruminant brings back up to chew again.
coprophagy: Eating feces. Some animals that ferment food after the small intestine do it to send food through a second time.

Check yourself: 41.4 Digestive systems shaped by diet

4 questions on 41.4 Digestive systems shaped by diet. Pick an answer to see if you got it, and why.

Question 1 of 4

A fossil skull of an extinct mammal has broad, flat cheek teeth with ridged, heavily worn grinding surfaces and small canines. Which diet do these teeth most likely indicate?

Question 2 of 4

Question 3 of 4

Tsetse flies feed only on vertebrate blood, which is short on several B vitamins. Flies given an antibiotic that kills the bacteria living inside them, without harming the flies, produce very few offspring. Treated flies whose blood meals are supplemented with B vitamins reproduce close to normally. What do these results show?

Question 4 of 4

Kangaroos ferment plant food with microbes in part of the stomach, before the small intestine. Capybaras ferment plant food in an enlarged cecum, after the small intestine, and regularly eat some of their own feces. Why would eating feces help a capybara more than a kangaroo?

0 of 4 answered

41.5 Hormones, blood sugar and appetite

pp. 891–895

On the AP exam? Yes

Topic 4.4 uses insulin and glucagon as its main example of negative feedback, Topic 4.1 covers hormones traveling in the blood to target cells, and Topic 8.2 covers storing extra energy. You won't need gastrin, secretin, CCK, ghrelin, leptin or PYY by name.

In the course: Topic 4.1 Cell Communication, Topic 4.2 Introduction to Signal Transduction, Topic 4.3 Signal Transduction Pathways, Topic 4.4 Feedback, Topic 8.2 Energy Flow Through Ecosystems (notes, videos and more questions)

Key points

The gut doesn't run nonstop. Each section gears up as food reaches it, driven by reflexes and by the gut's own nerve network, the enteric nervous system, which controls secretions and the muscle waves that move food along.
Hormones from the stomach and small intestine coordinate the work, traveling through the blood like all hormones. Gastrin from the stomach ramps up acid and enzyme output when a meal arrives. In the duodenum, acid sets off secretin (which brings bicarbonate from the pancreas) and fat and protein fragments set off CCK (which brings bile and pancreatic enzymes). A fatty meal raises both, which holds food in the stomach longer so the intestine isn't swamped.
Extra fuel is stored first as glycogen in liver and muscle, then as fat in adipose tissue. Fat packs about 9 kcal per gram, while carbohydrate and protein each give about 4, so fat is the most compact long-term store.
Blood glucose is held near a set point by negative feedback. After a meal, the pancreas releases insulin, which helps cells take up glucose and tells liver and muscle to store it as glycogen. Between meals, glucagon signals the liver to split glycogen and release glucose.
Appetite is controlled by hormones acting on the brain. Ghrelin from the stomach rises before meals and makes you hungry. PYY from the small intestine after meals, insulin and leptin from fat tissue all turn appetite down.
Leptin works over the long run: fat tissue releases it in proportion to how much fat there is, so gaining fat raises leptin and curbs appetite, while dieting lowers it and leaves you hungrier. Rare people born unable to make leptin are always hungry and become severely obese. Most people with obesity make plenty of leptin, but their brains respond to it weakly.
A drive to store fat whenever food was plentiful probably helped our ancestors survive lean times, which may be part of why weight gain is easy when food is always around. Newer obesity drugs mimic GLP-1, a gut hormone released after meals that boosts insulin release, slows the stomach and reduces appetite.

Key terms (15)

enteric nervous system: The network of nerve cells in the walls of your gut that controls its contractions and secretions, largely on its own.
gastrin: A stomach hormone that rises when a meal arrives and, by way of the blood, signals the stomach's own glands to make more acid and enzyme.
secretin: A duodenal hormone, set off by acid arriving from the stomach, that makes the pancreas send out bicarbonate to neutralize it.
cholecystokinin (CCK): A duodenal hormone, set off by fat and protein breakdown products, that makes the gallbladder squeeze out bile and the pancreas release its enzymes.
glycogen: A branched glucose polymer stored in liver and muscle cells as a quick-access fuel.
adipose tissue: Body fat: tissue whose cells store fat, the body's most compact energy reserve.
insulin: A pancreatic hormone released when blood glucose is high. It helps cells take up glucose and store it as glycogen.
glucagon: A pancreatic hormone released when blood glucose is low. It signals the liver to split glycogen into glucose and release it.
negative feedback: Regulation in which a change sets off a response that pushes the variable back toward its set point.
glucose homeostasis: Keeping blood glucose within a narrow range through meals, fasting and exercise.
ghrelin: A hormone made mainly by the stomach that rises before meals and makes you feel hungry.
leptin: A hormone made by fat tissue. Higher levels tell the brain there's plenty of stored fat and turn appetite down.
PYY: A hormone the small intestine releases once you've eaten that helps you feel full.
satiety: The feeling of being full that makes you stop eating.
obesity: Having so much stored body fat that it harms health, raising the risk of problems such as type 2 diabetes and heart disease.

Check yourself: 41.5 Hormones, blood sugar and appetite

4 questions on 41.5 Hormones, blood sugar and appetite. Pick an answer to see if you got it, and why.

Question 1 of 4

After an overnight fast, a healthy adult drinks a glucose solution. Blood glucose was measured for three hours (invented data). Time (min) | Blood glucose (mg/dL) 0 | 85 30 | 150 60 | 128 120 | 96 180 | 84 Which best describes the hormone changes between 30 and 120 minutes and their effect?

Question 2 of 4

A person has a mutation that changes the insulin receptor so that it can't bind insulin. The pancreas works normally. Which pattern would most likely be seen after a carbohydrate-rich meal?

Question 3 of 4

In an anesthetized animal, all the nerves leading to the duodenum and pancreas were cut. When dilute acid was placed in the duodenum, the pancreas still released its juice. An extract of cells from the duodenal lining, injected into a vein, had the same effect. Which conclusion do these results best support?

Question 4 of 4

In rats, blood levels of ghrelin, a hormone made mainly by the stomach, rise before regular feeding times and fall after eating. Researchers give rats a drug that blocks ghrelin receptors in the brain. Which result is most likely?

0 of 4 answered