Science · Grade 5 · Internal Systems of Living Things · Term 2

Waste Removal: The Excretory System

Students will explore how the body eliminates waste products through the excretory system.

• Ontario Curriculum Expectations
• 4-LS1-1

About This Topic

The excretory system keeps the body healthy by removing waste from blood and tissues to maintain balance. Grade 5 students focus on the kidneys, which filter blood plasma to remove urea, excess water, and salts, forming urine. Urine travels through ureters to the bladder for storage and exits via the urethra. Lungs, skin, and liver assist, but kidneys handle most liquid waste. This topic aligns with the internal systems unit, connecting to circulation and digestion.

Students compare animal excretory methods, such as birds producing uric acid paste versus mammals' liquid urine, and predict outcomes of malfunctions like kidney stones or failure, which cause toxin buildup, fatigue, and swelling. These explorations develop skills in comparing structures, hypothesizing, and explaining system interdependence.

Active learning suits this topic well. Students cannot see filtration directly, so models with filters and dyes, animal waste examinations, and simulations reveal processes. Hands-on work encourages predictions, observations, and discussions that solidify concepts and spark curiosity about body maintenance.

Key Questions

1. Explain the role of the kidneys in filtering waste from the blood.
2. Compare how different animals eliminate waste from their bodies.
3. Hypothesize the consequences of a malfunctioning excretory system.

Learning Objectives

• Explain the function of the kidneys in filtering urea and excess water from the blood.
• Compare the methods of waste elimination used by mammals and birds, citing specific waste products.
• Hypothesize the physiological consequences of a malfunctioning excretory system, such as kidney failure.
• Identify the roles of the lungs, skin, and liver in assisting the excretory system.
• Analyze the interdependence of the excretory system with the circulatory and digestive systems.

Before You Start

The Circulatory System

Why: Students need to understand how blood transports substances throughout the body to grasp how the kidneys filter blood.

The Digestive System

Why: Students should know how food is processed and how waste is generated to understand what the excretory system removes.

Key Vocabulary

Excretory System	The body system responsible for eliminating waste products and excess water from the body.
Kidneys	Bean-shaped organs that filter waste products and excess water from the blood to produce urine.
Urea	A waste product formed in the liver from the breakdown of proteins, which is then removed from the blood by the kidneys.
Urine	The liquid waste product, consisting of water, urea, and salts, that is filtered from the blood by the kidneys.
Bladder	A muscular sac that stores urine before it is eliminated from the body.

Watch Out for These Misconceptions

Common Misconception

Kidneys make urine only from dirty blood.

What to Teach Instead

Kidneys filter clean blood continuously, reabsorbing needed water and nutrients while removing wastes like urea from protein breakdown. Coffee filter demos let students see selective removal firsthand, correcting the idea through observation and group talk.

Common Misconception

All waste leaves through bowels.

What to Teach Instead

Excretory system handles blood-filtered wastes via urine; bowels manage solid food remnants. Animal waste comparisons clarify distinct paths, with peer posters helping students sort and debate roles.

Common Misconception

Body can store waste harmlessly.

What to Teach Instead

Wastes accumulate and poison cells without removal, causing illness. Malfunction simulations show buildup effects visually, prompting hypotheses and discussions that reveal homeostasis needs.

Active Learning Ideas

Hands-On: Kidney Filter Model

Provide coffee filters as kidneys, sand and charcoal as filtering materials, and dyed water as blood with 'wastes.' Students layer filters in funnels, pour liquid through, and collect filtrate in cups. Groups compare before-and-after samples, noting clearer output, then discuss kidney parallels.

30 min·Small Groups

Compare: Animal Excretion Charts

Distribute images or samples of animal wastes: fish slime, bird paste, mammal urine. In pairs, students chart waste type, composition, and removal method on T-charts. Share findings class-wide to identify patterns like water conservation in deserts.

35 min·Pairs

Simulation Game: System Malfunction Role-Play

Assign roles: kidneys, blood, wastes, bladder. Use props like balls for wastes. 'Healthy' rounds show smooth removal; 'malfunction' rounds pile up wastes, acting symptoms. Debrief on consequences like poisoning.

25 min·Small Groups

Tracking: Daily Fluid Balance Log

Students log intake/output over two days using cups and charts. Calculate balance, hypothesize links to kidney work. Class graph reveals patterns, tying personal data to system function.

40 min·Individual

Real-World Connections

• Nephrologists are medical doctors who specialize in kidney health and treat conditions like kidney stones or kidney disease, often recommending dietary changes or dialysis for patients.
• Water treatment plants use filtration and chemical processes similar to how kidneys filter blood, ensuring safe drinking water by removing impurities and waste products from raw water sources.

Assessment Ideas

Quick Check

Present students with a diagram of the human excretory system. Ask them to label the kidneys, ureters, bladder, and urethra. Then, ask them to write one sentence describing the main function of the kidneys.

Discussion Prompt

Pose the question: 'What might happen if a person's kidneys stopped working?' Guide students to discuss potential consequences such as toxin buildup, swelling, and fatigue, connecting these to the kidneys' filtering role.

Exit Ticket

Provide each student with a card asking them to compare waste removal in a human versus a bird. They should name the primary waste product for each and briefly describe its form (e.g., liquid urine vs. paste).

Frequently Asked Questions

How do kidneys filter blood in simple terms for Grade 5?

Explain kidneys as busy sieves processing 180 liters of blood daily, keeping good stuff like glucose and water while flushing urea and extras into urine. Use everyday analogies: kidneys act like a coffee filter straining grounds from brew. Hands-on models reinforce this, as students pour dyed water through sieves and measure changes, building accurate mental images of selective filtration.

What activities compare animal waste removal?

Use charts with photos of fish gills expelling ammonia, bird cloacas dropping uric acid, and mammal bladders releasing urine. Pairs sort by habitat needs, like dry-adapted animals minimizing water loss. Class shares highlight evolutionary links, deepening appreciation for diverse solutions while tying to Ontario curriculum expectations.

How does active learning benefit excretory system lessons?

Active approaches make invisible processes visible through kidney models, waste simulations, and logs. Students predict outcomes, test with materials like filters and dyes, observe results, and revise ideas in groups. This cycle boosts retention, corrects misconceptions via evidence, and connects abstract functions to real body needs, aligning with inquiry-based science.

What happens if the excretory system malfunctions?

Issues like infections or blockages prevent waste removal, leading to toxin buildup, swelling, pain, and organ strain. Students hypothesize via role-plays: excess 'wastes' cause chaos. Discuss real cases like dialysis needs, emphasizing prevention through hydration and diet, fostering health awareness alongside science concepts.