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By the end of this section, you will be able to:
  • Explain the processes of digestion and absorption
  • Compare and contrast different types of digestive systems
  • Explain the specialized functions of the organs involved in processing food in the body
  • Describe the ways in which organs work together to digest food and absorb nutrients

Animals obtain their nutrition from the consumption of other organisms. Depending on their diet, animals can be classified into the following categories: plant eaters (herbivores), meat eaters (carnivores), and those that eat both plants and animals (omnivores). The nutrients and macromolecules present in food are not immediately accessible to the cells. There are a number of processes that modify food within the animal body in order to make the nutrients and organic molecules accessible for cellular function. As animals evolved in complexity of form and function, their digestive systems have also evolved to accommodate their various dietary needs.

Herbivores, omnivores, and carnivores

Herbivores are animals whose primary food source is plant-based. Examples of herbivores, as shown in [link] include vertebrates like deer, koalas, and some bird species, as well as invertebrates such as crickets and caterpillars. These animals have evolved digestive systems capable of handling large amounts of plant material. Herbivores can be further classified into frugivores (fruit-eaters), granivores (seed eaters), nectivores (nectar feeders), and folivores (leaf eaters).

Left photo shows a buck with antlers. Right photo shows a black, yellow, and white striped caterpillar eating a leaf.
Herbivores, like this (a) mule deer and (b) monarch caterpillar, eat primarily plant material. (credit a: modification of work by Bill Ebbesen; credit b: modification of work by Doug Bowman)

Carnivores are animals that eat other animals. The word carnivore is derived from Latin and literally means “meat eater.” Wild cats such as lions, shown in [link] a and tigers are examples of vertebrate carnivores, as are snakes and sharks, while invertebrate carnivores include sea stars, spiders, and ladybugs, shown in [link] b . Obligate carnivores are those that rely entirely on animal flesh to obtain their nutrients; examples of obligate carnivores are members of the cat family, such as lions and cheetahs. Facultative carnivores are those that also eat non-animal food in addition to animal food. Note that there is no clear line that differentiates facultative carnivores from omnivores; dogs would be considered facultative carnivores.

Top photo shows a lion. Bottom photo shows a ladybug.
Carnivores like the (a) lion eat primarily meat. The (b) ladybug is also a carnivore that consumes small insects called aphids. (credit a: modification of work by Kevin Pluck; credit b: modification of work by Jon Sullivan)

Omnivores are animals that eat both plant- and animal-derived food. In Latin, omnivore means to eat everything. Humans, bears (shown in [link] a ), and chickens are example of vertebrate omnivores; invertebrate omnivores include cockroaches and crayfish (shown in [link] b ).

Top photo shows a bear. Bottom photo shows a crayfish.
Omnivores like the (a) bear and (b) crayfish eat both plant and animal based food. (credit a: modification of work by Dave Menke; credit b: modification of work by Jon Sullivan)

Questions & Answers

Hello how are you every body
Sitali Reply
join the conversation
Sitali
l am fine every body
Memiru
I'm very fine_hopefully everyone is fine
Rorisang
what is meant by submicroscopic?
anji Reply
what is anabolic and catabolic
Jonathan
hi
Alpha
hi berther
Memiru
hallo
Memiru
what is the meaning of biology
Dorathy Reply
biology is scientific study of living things
GUYO
what is chromosomes?
Mabiya Reply
it is a cell structure that contains DNA histones protein and other structural proteins
Ekechi
what is DNA
Kashah
what is liver
Hassan Reply
liver is an organ in the body that meterbolise nutrients and produce bile.
Ekechi
what is the function of granum?
Gulfam
what is the faction of liver cancer
Kashah
What is biology
Eric Reply
Biology is you
muayad
Biology is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms, development and. evolution
Suzette
biology is the study of living things and none living things
Ekechi
study of living organisms
anji
The mamalian endoskeleton has 206 bones
kaazim Reply
hii
Hannah
hi
Suzette
how you
Hannah
good thanks
Suzette
have you done the actual course?
Suzette
How many bones do human body have?
moses Reply
I don't know please help me
Kisito
206
Waneh
206
Moses
206
anji
what are these geneti materials
ONELIA Reply
Name five parts of female reproductive system and state the function of each part
Angel Reply
What is biology
Angel
What is biology
Angel
biology is the study of all living organisms
ketchem
Ok
Angel
Name five parts of female reproductive system and state the function of each part
Angel
What is the meaning of respiration
Idriss Reply
the act or process of breathing .
Suzette
the process is very long as I know
Idriss
do you want more details ?
Suzette
yes offcourse
Smiso
what does the term diploid and haploid mean?
ONELIA
what is virgina
Shebas Reply
A female reproductive organs
Julius
fuvu LA binadam linamifupa mingapi?
Hamis Reply
explain dicot n monocot plant
Henry Reply
Di= 2cotiledon mono=cotiledon
muayad
Mono = 1 cotiledon
muayad
what is virginia
Shebas
A Virginia is a part of a female ,the passage of a child during child birth, receiver of the penis and the passage of menstral flow
Idriss
what is biology
Hassan Reply
what is liver
Hassan
Biology is the study of living organisms
Gifty
is the study of life of living organisms
Chansa
study all about organisms like their reproduction, evolution , behaviour Physiology, etc
Ubaid
this is what we call "life"@
Chansa
is the study of living organisms on earth
okubasu
It is the study of living organism
Idriss
Biology is the study of all living organisms
ketchem
what is copulation
ketchem

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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