Name: water balance and waste removal in animals
Uploaded: 2025-10-23T11:49:08.000Z
Duration: 2 min 12 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Life Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-2

What Are Osmoregulation and Excretion?

To support bodily functions, animals regularly consume food and water. Material that cannot be used is excreted as waste. One of the most significant waste forms is nitrogen, a by-product of the breakdown of proteins and nucleic acids. Nitrogen tends to form ammonia in the body which is toxic, and must be properly disposed of. 
Some animals directly excrete ammonia. Others first convert it into a less toxic form, like urea or uric acid. The variety of excretory systems allow animals to balance the conservation of energy and water.
What is maintained in the body is as important as what is removed from it. Regardless of diet, weather, and other external conditions, bodily systems must balance the level of water and dissolved substances called solutes. This is achieved through osmoregulation.
Osmosis is the tendency of water to move across a semi-permeable membrane from solutions with lower ion concentrations, or osmolarities, to those with higher ion concentrations. Bodily fluids, like plasma, and fluids inside and outside of cells are separated by such membranes. Animals control internal solute and water levels by osmoconforming or osmoregulating.
Osmoconformers have an internal osmo

what are osmoregulation and excretion?

Organisms must keep bodily fluids at a constant temperature and pH while maintaining specific solute concentrations in order to support life functions. Osmoregulation is the process that balances solute and water levels.

Osmosis is the tendency of water to move from solutions with lower ion concentrations, or osmolarities, to those with higher ion concentrations. Osmosis occurs in response to differences in the molecular concentrations of solutions separated by a semipermeable membrane.

Bodily fluids, which are separated by such membranes, contain water, non-electrolytes, and electrolytes&#8212;solutes that dissolve into ions in water. Both electrolytes and non-electrolytes influence osmotic balance. However, since the more important factor to osmosis is solute number, rather than size, the contribution of electrolytes is more significant.

Unlike water, electrolytes cannot diffuse passively through membranes but rely on facilitated diffusion and active transport. In facilitated diffusion, protein-based channels move solutes across membranes. Conversely, energy is used to move ions against concentration gradients in active transport.

When animals ingest food, material that cannot be used is excreted from the body. Excretory systems in nature involve tradeoffs between conserving energy and water.

Nitrogen is among the most significant kinds of waste in the body. Excess nitrogen forms ammonia, which is toxic and must be discarded. Some animals directly excrete ammonia; others first convert it into urea or uric acid, which are less toxic. Ammonia conversion requires more energy than direct excretion, however, it conserves more water.

Transport epithelia often mediate osmoregulation and excretion. These specialized cells move solutes and are found in excretory organs throughout the animal kingdom: from insect Malpighian tubules to fish gills to vertebrate kidneys.

Typically organized in tube-shaped networks with large surface areas, transport epithelia often assist with both water balance and waste removal. For example, some seabirds have nasal glands that remove salt from the blood and excrete it from the nostrils, enabling them to consume seawater.

Organisms must keep bodily fluids at a constant temperature and pH while maintaining specific solute concentrations in order to support life functions. ...

Education

JoVE Core

Biology

Human Biology

Osmoregulation and Excretion

KEY TERMS AND CONCEPTS

water balance and waste removal in animals

Water balance and waste removal in animals help keep body fluids stable. Organisms must maintain a constant temperature and pH, along with specific solute levels, to support life functions. Osmoregulation is the process that keeps water and solute levels in balance.

Osmosis is the movement of water from solutions with lower ion concentrations, or lower osmolarities, to solutions with higher ion concentrations. It happens because two solutions are separated by a semipermeable membrane. Bodily fluids contain water, non-electrolytes, and electrolytes, which are solutes that dissolve into ions in water.

Both electrolytes and non-electrolytes affect osmotic balance. However, osmosis depends more on the number of solute particles than on their size. That makes electrolytes especially important. Electrolytes also cannot pass freely through membranes. They move by facilitated diffusion through protein channels or by active transport, which uses energy to move ions against a concentration gradient.

Animals must also remove material that cannot be used after food is ingested. This is part of excretion. Excretory systems face a tradeoff between saving energy and saving water. Nitrogen waste is a major example. Extra nitrogen can form ammonia, which is toxic and must be removed.

Some animals excrete ammonia directly. Others convert it into urea or uric acid first. These forms are less toxic, but making them requires more energy. The advantage is that they conserve more water.

Transport epithelia often carry out osmoregulation and excretion. These specialized cells move solutes and are found in excretory organs across the animal kingdom. Examples include insect Malpighian tubules, fish gills, and vertebrate kidneys. They are often arranged in tube-like networks with large surface areas, and they help with both water balance and waste removal. Some seabirds also have nasal glands that remove salt from the blood and excrete it through the nostrils, which lets them drink seawater.

Water Balance and Waste Removal in Animals

water-balance-and-waste-removal-in-animals

kidney structure

How Kidneys Filter Blood and Make Urine

The kidneys are two bean-shaped organs in the upper abdomen that filter blood and help keep water and electrolytes in balance. They receive blood from the heart through the renal arteries, and they send filtered blood away through the renal veins. The renal arteries enter the kidney at the hilum, the concave inner surface of the bean shape. From there, they branch into smaller vessels and capillaries. This branching helps move blood through the kidney for filtering. The thick outer layer of...

filtration and urine formation

Kidney Nephrons and Urine Control

Kidney nephrons and urine control depend on filtration, reabsorption, secretion, and excretion. The kidneys filter nearly 180 liters of blood each day. They first remove water and dissolved substances, then return nearly all of the filtrate to the bloodstream with help from osmoregulatory hormones. This process clears wastes and toxins while keeping water and electrolyte levels balanced. Most of these jobs happen in the tiny nephrons inside the kidneys. Blood enters the nephron’s renal...

urea cycle

Liver Detox and the Urea Cycle

The urea cycle is a liver pathway that converts ammonia into urea. Ammonia is a toxic waste product made during protein catabolism. Land animals must change ammonia into the less toxic urea so the kidneys can remove it in urine. Marine animals can excrete ammonia directly because water dilutes it to safer levels. The cycle has five main steps. First, ammonia is converted to carbamoyl phosphate. Next, ornithine is added as carbamoyl phosphate becomes citrulline. Citrulline then forms...

hormonal regulation

Renin-Angiotensin Control of Blood Pressure

Renin-angiotensin control of blood pressure is a hormone system that helps the kidneys manage water and electrolytes. It also supports osmoregulation, which is the body’s control of water and salt balance. The system begins in the kidneys near the renal corpuscle, where juxtaglomerular cells sit beside the afferent and efferent blood vessels. As nephrons filter blood, these cells monitor blood pressure. If pressure drops, they release renin into the bloodstream. Renin acts on angiotensinogen,...

osmoregulation in fishes

Fish Water and Salt Balance

Fish water and salt balance helps keep their cells from swelling or shrinking in changing environments. Cells in a hypotonic, or low-salt, fluid can swell and burst. Cells in a hypertonic fluid, which has a higher salt concentration, can shrivel and die. Fish use osmoregulation to control water and dissolved ions such as sodium and chloride. Osmosis is the movement of water across a membrane that lets water pass. Water moves in both directions, but the net flow goes toward the side with more...

osmoregulation in insects

Malpighian Tubules and Water Saving

Malpighian tubules help insects remove waste and conserve water. These specialized structures are found in the digestive systems of many arthropods, including most insects. They are usually arranged in pairs, and their twisted shape gives them more surface area. The tubules extend from the digestive tract, usually between the midgut and hindgut, into the hemolymph. Hemolymph is the fluid that mixes blood and interstitial fluid in insects and other arthropods, and in most mollusks. Unlike many...

comparative excretory systems

Nitrogen Waste in Animal Excretion

Animals use different excretory strategies to remove waste from the body. These strategies matter because most waste must be dissolved in water before it can leave the body. That means excretion is closely tied to water balance. Nitrogenous wastes are some of the most important animal wastes. Nitrogen is released when proteins and nucleic acids are broken down for energy or turned into carbohydrates and fats. Proteins become amino acids, and nucleic acids become nitrogenous bases. The...

Water balance and waste removal in animals help keep body fluids stable. Organisms must maintain a constant temperature and pH, along with specific solute levels, to support life functions. Osmoregulation is the process that keeps water and solute levels in balance. Osmosis is the movement of water from solutions with lower ion concentrations, or lower osmolarities, to solutions with higher ion concentrations. It happens because two solutions are separated by a semipermeable membrane. Bodily...

key terms and concepts

Learn how animals balance water and solutes, move ions across membranes, and remove nitrogen waste through excretion, kidneys, gills, and other transport epithelia.

Water Balance and Waste Removal in Animals | JoVE K12

JoVE Core series brings biology to life through over 300 concise and easy-to-understand animated video lessons that explain key concepts in biology, plus more than 150 scientist-in-action videos that show actual research experiments conducted in today’s laboratories.

biology

HS-LS1-3

new-york-state-science-learning-standards

New York State Science Learning Standards

Structure and Function

HS-LS1-2.

myJoVE Corporation

Characteristics of Life

Biology is a natural science that studies life and living organisms, including their structure, function, development, interactions, evolution, ...

https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/10647.jpg

Cell Structure

Background
Cells represent the most basic biological units of all organisms, whether it be simple, single-celled organisms like bacteria, or large, ...

Visualizing Onion and Cheek Cells
ExpandImmediately before the experiment, wash and peel onion bulbs for the class.
Remove the entire brown outer skin and ...

Visualizing Onion and Human Cells
ExpandIn this experiment you will prepare different types of cells from a plant and animal, onion and human ...

What are Cells?

Cell Diversity

The concept of a cell started with microscopic observations of dead cork tissue by Robert Hooke in 1665. Hooke coined the term &#34;cell&#34; based on the ...

Cytoplasm

The cytoplasm consists of organelles and a framework of protein scaffolds called the cytoskeleton suspended in an aqueous solution, the cytosol. The ...

The Nucleus

The nucleus is a membrane-bound organelle that acts as a control center in a eukaryotic cell. It contains chromosomal DNA, which controls gene expression ...

The Central Dogma

The DNA Helix

Nucleic Acids

DNA as a Genetic Template

Structure of a Gene

A gene is the fundamental unit of heredity. Every individual has two copies of each gene, one inherited from each parent. Although most people contain the ...

Chromosome Structure

Base-pairing and DNA Repair

What is Gene Expression?

A gene is a stretch of DNA that serves as the blueprint for functional RNAs and proteins. Since DNA is comprised&#160; of nucleotides and proteins are ...

RNA Structure

The basic structure of RNA consists of a string of ribonucleotides attached by phosphodiester bonds. Although most RNA is single-stranded, it can form ...

Protein Families

Types of RNA

Three main types of RNA are involved in protein synthesis: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). These RNAs perform diverse ...

Conservation of Protein Domains

Transcription

Transcription is the synthesis of RNA from a DNA sequence by RNA polymerase. It is the first step in producing a protein from a gene sequence. ...

Globular and Fibrous Proteins

Translation

Translation is the process of synthesizing proteins from the genetic information carried by messenger RNA (mRNA). Following transcription, it constitutes ...

Intrinsically Disordered Proteins

Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that ...

Protein Complex Assembly

Protein and Protein Structures

Conjugated Proteins

Proteins: From Genes to Degradation

Amyloid Fibrils

What are Proteins?

Proteins are polymers of amino acids linked together by peptide bonds. Proteins and polypeptides are interchangeably used to refer to long chains of amino ...

Ligand Binding Sites

Protein Organization

Proteins are polymers of amino acid residues. They are versatile and responsible for different cellular functions, including DNA replication, molecular ...

Protein-Protein Interfaces

Protein Folding

Proteins are chains of amino acids linked together by peptide bonds. Upon synthesis, a protein folds into a three-dimensional conformation, critical to ...

Conserved Binding Sites

Cofactors and Coenzymes

Enzymes are proteins made of amino acids. The functional group of each constituent amino acid catalyzes a wide variety of chemical reactions via ionic ...

Cooperative Allosteric Transitions

Protein Kinases and Phosphatases

GTPases and their Regulation

Covalently Linked Protein Regulators

protein-complexes-with-interchangeable-parts

Protein Complexes with Interchangeable Parts

Mechanical Protein Function

Structural Protein Function

Protein Networks

Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells. [Assessment Boundary: Assessment does not include identification of specific cell or tissue types, whole body systems, specific protein structures and functions, or the biochemistry of protein synthesis.]

HS-LS1-1

Levels of Organization

Biological organization is the classification of biological structures, ranging from atoms at the bottom of the hierarchy to the Earth&#x27;s biosphere. ...

Animal and Plant Cell Structure

Animal and plant cells not only differ in their structure, function, and mode of nutrition but also in how they reproduce, specialize, and organize into ...

structural-organization-of-the-human-body-an-overview

Structural Organization of the Human Body: An Overview

It is convenient to consider the body&#39;s structures in terms of fundamental levels of organization that increase in complexity: subatomic particles, ...

Overview of Human Digestion

The human body contains a monogastric digestive system. In a monogastric digestive system, the stomach only contains one chamber in which it digests food. ...

Anatomy of the Intestines

Although digestion of proteins, carbohydrates, and lipids may begin in the stomach, it is completed in the intestine. The absorption of nutrients, water, ...

Accessory Organs

Accessory organs are those that participate in the digestion of food but do not come into direct contact with it like the mouth, stomach, or intestine do. ...

Lipid Digestion

Lipids are large molecules that are generally not water-soluble. Since most of the digestive enzymes in the human body are water-based, there are specific ...

Protein Digestion

Protein digestion begins in the stomach, where the highly acidic environment can easily disrupt protein structure by exposing the peptide bonds of ...

Carbohydrate Digestion

Carbohydrate digestion and metabolism break down simple and complex carbohydrates from food into saccharides (i.e., sugars) for the body to use as energy. ...

Overview of the Nervous System

Overview

The nervous system is the collection of specialized cells responsible for maintaining an organism&#x2019;s internal environment and coordinating ...

The Parasympathetic Nervous System

Overview

The parasympathetic nervous system is one of the two major divisions of the autonomic nervous system. This parasympathetic system is responsible ...

The Sympathetic Nervous System

Overview

The sympathetic nervous system&#x2014;one of the two major divisions of the autonomic nervous system&#x2014;is activated in times of stress. It ...

Oogenesis

In human women, oogenesis produces one mature egg cell or ovum for every precursor cell that enters meiosis. This process differs in two unique ways from ...

What is a Sensory System?

Sensory systems detect stimuli&mdash;such as light and sound waves&mdash;and transduce them into neural signals that can be interpreted by the nervous ...

Fertilization

During fertilization, an egg and sperm cell fuse to create a new diploid structure. In humans, the process occurs once the egg has been released from the ...

What is the Skeletal System?

Overview

The adult human skeleton comprises 206 bones that are connected through cartilage, tendons, and ligaments. The skeleton provides a rigid ...

an-introduction-to-the-zebrafish-danio-rerio

An Introduction to the Zebrafish: Danio rerio

Zebrafish (Danio rerio) are small freshwater fish that are used as model organisms for biomedical research. The many strengths of these fish include their ...

Physiology of the Circulatory System

Homeostasis
Conditions in the external environment of an organism can change rapidly and drastically. To survive, organisms must maintain a fairly ...

Anatomy of the Circulatory System

The human circulatory system consists of blood, blood vessels that carry blood away from the heart, around the body, and back to the heart, and the heart ...

Measuring Blood Pressure
ExpandTo prepare for the blood pressure exercise, simply place the appropriate number of alcohol swabs, sphygmomanometers, and ...

Anatomy of the Heart

The human heart is made up of three layers of tissue that are surrounded by the pericardium, a membrane that protects and confines the heart. The ...

Measuring Circulatory System Function in Humans
ExpandBefore starting the experiment go to the front of the room and collect an alcohol swab, a ...

Blood Flow

Blood is pumped by the heart into the aorta, the largest artery in the body, and then into increasingly smaller arteries, arterioles, and capillaries. The ...

Blood Withdrawal I

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN
Blood collection is a common requirement for ...

Kidney Structure

The kidneys are two large bean-shaped organs located in the upper abdomen. They filter the blood several times a day to remove toxins and rebalance water ...

Blood Withdrawal II

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN
The collection of blood from mice and rats for ...

What is the Immune System?

Overview

The immune system comprises diverse biological structures and processes that protect the body from disease. These processes can be classified ...

Bone Remodeling

Bone remodeling is a continuous and balanced process of bone resorption by osteoclasts and bone formation by osteoblasts. In adults, it helps maintain ...

Spermatogenesis

Spermatogenesis is the process by which haploid sperm cells are produced in the male testes. It starts with stem cells located close to the outer rim of ...

Bone Structure

Within the skeletal system, the structure of a bone, or osseous tissue, can be exemplified in a long bone, like the femur, where there are two types of ...

Breathing

The process of breathing, inhaling and exhaling, involves the coordinated movement of the chest wall, the lungs, and the muscles that move them. Two ...

Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. [Clarification Statement: Emphasis is on functions at the organism system level such as nutrient uptake, water delivery, and organism movement in response to neural stimuli. An example of an interacting system could be an artery depending on the proper function of elastic tissue and smooth muscle to regulate and deliver the proper amount of blood within the circulatory system.] [Assessment Boundary: Assessment does not include interactions and functions at the molecular or chemical reaction level.]

What is Homeostasis?

Maintaining homeostasis requires that the body continuously maintain its internal conditions. Each physiological condition has a particular set point, ...

Negative and Positive Feedback

Homeostatic Imbalance

Homeostasis is the maintenance of a stable internal environment within the body, which is crucial for the proper functioning of cells, tissues, organs, ...

pH Homeostasis

Acid-base homeostasis is essential for maintaining normal physiological activities in humans. The pH of various body fluids is strictly regulated because ...

Positive and Negative Feedback Loops

Animal organs and organ systems constantly adjust to internal and external changes through a process called homeostasis (&#34;steady state&#34;). Examples ...

Cell Signaling Feedback Loops

Positive and negative feedback loops are crucial for regulating biological signaling systems. These feedback loops are processes that connect output ...

Regulation of Hormone Secretion

Hormone secretion is regulated by different types of signals, including neural, humoral, and hormonal stimuli.
Neural stimuli are triggered by the ...

Autoregulation of Blood Flow

Autoregulation is the ability of tissues to maintain blood flow based on their metabolic requirements. It ensures optimal blood flow to support both ...

Neural Regulation of Blood Pressure

The nervous system regulates blood pressure through baroreceptor and chemoreceptor reflexes.
Baroreceptors in the carotid sinuses and aortic arch respond ...

Regulation of Metabolism

Cellular needs and conditions vary from cell to cell and change within individual cells over time. For example, the required enzymes and energetic demands ...

Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis. [Clarification Statement: Examples of investigations could include heart rate response to exercise, stomate response to moisture and temperature, and root development in response to water levels.] [Assessment Boundary: Assessment does not include the cellular processes involved in the feedback mechanism.]

Water Balance and Waste Removal in Animals

Description

Transcript

Tags

More videos by Standards