7th Grade Science
Notes > OBTAINING ENERGY & REMOVING WASTE
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Energy from Food
Organisms eat for several reasons, and the process of deciding what to eat and when to eat it is influenced by various factors. While humans can survive for weeks without food, the sensation of hunger arises just a few hours after a meal. The body's need for food is driven by the fact that food contains energy and nutrients necessary for survival.
The energy content of food is measured in Calories. A Calorie (Cal) is the amount of energy required to raise the temperature of 1 kg of water by 1°C. Different foods contain varying amounts of energy. For example, one grape contains 2 Cal, while a slice of cheese pizza may have 220 Cal. The body obtains energy from all types of food.
Every activity an organism performs requires energy. Activities such as riding a bike or even sleeping utilize energy. The digestive system processes the food consumed and releases energy from it. This energy is utilized for cellular processes and all activities undertaken by the organism. The amount of energy an individual needs depends on factors like weight, age, activity level, and gender. For instance, a person weighing 68 kg (149 lb) typically burns more calories than someone weighing 45 kg (99 lb). Activities with higher intensity, such as playing soccer, require more energy than less strenuous activities like playing a video game.
Food is composed of nutrients, which are the components utilized by the body for growth and survival. Nutrients provide energy and materials for cellular development, growth, and repair. There are several types of nutrients, including proteins, fats, carbohydrates, vitamins, and minerals.
Waste Removal
The excretory system, consisting of various body systems such as the digestive system, respiratory system, and integumentary system (skin), is responsible for collecting and eliminating waste from the body. The digestive system eliminates solid waste, while the urinary system processes and removes liquid waste (urine) through the kidneys, ureters, bladder, and urethra.
The Digestive System
Humans require food, water, and oxygen for survival, and the nutrients present in food are absorbed and utilized by the body through the process of digestion.
Digestion is the process by which food is mechanically and chemically broken down into small particles and molecules that the body can absorb and utilize. It involves four main stages: ingestion, digestion, absorption, and elimination.
Types of Digestion: Before the body can absorb nutrients from food, the food must undergo digestion, which can be of two types: mechanical and chemical. Mechanical digestion involves physically breaking down food into smaller pieces through actions like chewing, mashing, and grinding with the teeth and tongue. This creates smaller food particles that are easier to swallow and have a larger surface area for chemical digestion. Chemical digestion involves the breakdown of food into small molecules through chemical reactions.
Digestive Process: The journey of food through the organs and tissues of the digestive system begins with ingestion in the mouth. The mouth mechanically and chemically digests food through chewing, saliva production, and the action of enzymes. The partially digested food then passes through the esophagus, aided by peristalsis (muscle contractions), and enters the stomach. In the stomach, food storage and chemical digestion take place. The stomach's acidic environment, along with enzymes like pepsin, breaks down proteins. The partially digested food then moves into the small intestine, where most chemical digestion and nutrient absorption occur. The small intestine has folds and villi that increase its surface area for absorption. Any remaining undigested material passes into the large intestine, where water absorption takes place, and the waste products of digestion form feces. The feces are eliminated from the body through the rectum and anus.
The Urinary System
Ever wondered where your pee goes? Buckle up, because we're about to explore the amazing urinary system, your body's built-in waste disposal unit!
Organs:
Kidneys: These bean-shaped champs filter waste from your blood, making pee. Imagine them like tiny factories!
Ureters: Think of these as two thin tubes, like highways carrying pee from the kidneys to...
The Bladder: A muscular balloon that stores pee until it's time to go. Picture it like a stretchy water tank!
The Urethra: This final tube is the exit ramp, letting pee leave your body when you say "go!"
The Process:
Filtering Fun: Kidneys remove waste and extra water, creating urine.
Highway Hustle: Ureters whisk urine away from the kidneys.
Bladder Time: Urine stays in the bladder until it's full (you feel the urge to go!).
Let it Flow: When you urinate, muscles squeeze the bladder, pushing urine out through the urethra.
Other than feces and urine our body gets rid of other “WASTES”.
Carbon Dioxide: Imagine your lungs as air filters. As you breathe, they take in oxygen and release carbon dioxide, a waste product of your cells. The lungs exhale it, keeping your body clean and functioning well.
Sweat: Your skin sweats out water, salts, and small amounts of other waste products. Sweating helps regulate your body temperature and gets rid of excess water and salts you don't need. Imagine sweat as the "dirty water" your body needs to drain.
Lungs and skin work alongside the kidneys, liver, and digestive system to eliminate different types of waste.
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