الأسبوع 12 · الموضوع ٢-٣ (٢): ضغط الدم والرياح وسرعة الرياح والأنسجة النباتية البسيطة والرطوبة وتأثيرها في الإنسان والكائنات الحية وتنظيم الماء في الجسم · 3 دروس
1
Blood pressure and the wind
Integrated Science Sec 1 Term 1, Unit 2: pp. 90–97
GoalRead a blood pressure value, and explain why wind blows from high to low pressure.
New words
blood pressure · the force of the blood on the walls of the blood vesselssystolic · the higher number, when the heart contractsdiastolic · the lower number, when the heart relaxeswind · air moving from a place of higher pressure to one of lower pressure
Explanation
Blood pressure is how hard the moving blood pushes on the inside of the vessel walls, for each unit of area. It is written as two numbers in mmHg: the systolic pressure (when the heart contracts) over the diastolic pressure (when the heart relaxes). A healthy adult’s normal value is about 120/80 mmHg, read “120 over 80”. A steady pressure delivers oxygen and nutrients to the cells. Questions about your own blood pressure go to a doctor. Wind: when the pressure differs between two places at the same level, air flows from the place of higher pressure towards the place of lower pressure. A wind is named after the place it comes from, not “from cold to hot”. The polar winds are cold, dry winds that blow from the high pressure around the poles to the lower pressure in the sub-polar regions. Strong winds change how heat and moisture are spread, and can break stems or tear leaves unless plants have strong tissues.
Reading
Systolic
Diastolic
typical healthy adult
120 mmHg
80 mmHg
example, read “140 over 90”
140 mmHg
90 mmHg
Worked examples
Read a blood pressure of 118/76 mmHg. The systolic pressure is 118 mmHg and the diastolic 76 mmHg. The systolic is always the larger number. The difference is 118 − 76 = 42 mmHg.
Which way does the air move? Place A has 1015 mbar and place B has 1008 mbar at the same level. The air moves from A (high) to B (low), and the pressure difference is 1015 − 1008 = 7 mbar. The wind blows from A.
Why are polar winds cold and dry? They start over the poles, where the air is cold and holds little moisture, and blow toward the lower pressure in the sub-polar regions.
Class activity
Card game, in pairs. Make six cards, each with a place name you invent and a pressure in mbar (for example 1020, 1005, 1012). Draw two cards and say aloud which place is high and which is low, and which way the air moves. Write each result as “from ... to ...”. Add a column that says which place the wind is named after.
Practice
1
Which number is larger in a blood pressure reading, and what does it show?
The systolic, which shows the pressure when the heart contracts.
2
Place X has 1002 mbar and place Y has 1011 mbar. From which place to which does the air move?
From Y to X, from high to low pressure.
3
Why do strong winds need strong plant tissues?
Without them stems could break and leaves tear.
4
Give the typical blood pressure of a healthy adult.
